Tool Changers

[thewoodcrafter]

Does anyone know if ShopBot sells a tool changer?
I am looking at production runs of MDF doors that require 4 tools and a tool changer sure would be a help.
Has anyone built a tool changer for there machine?
How would the position of the tool rack be addressed if the 0,0 position is changed for various parts?
We plan on cutting doors from 4x10 sheets then go back and carve the center panel of some of them. The carved doors would be placed 1 at a time with 0,0 in the center of the door.
Can the table limits be used somehow for this?

[cip]

Yes, ShopBot sell a tool changer. Last time I checked it was around $16,000.00 plus install and training.

Mike

[thewoodcrafter]

Well $16,000 is out of the question.
Thats not even an option.

Has anyone built one?

[patricktoomey]

I think the biggest issue is that you need a spindle that is already setup for a tool changer. It needs to have the quick release collet system that accepts the collet assembly with the bit installed in it. A regular spindle collet assembly can't work with a tool changer. It has always seemed to me that it wouldn't be rocket science to make a stepper controlled rotating tray to hold tools. If you had a quick change spindle, it seems like something that could be done if you had the knowledge and the patience.

[thewoodcrafter]

You are right about a quick release.
A guess I thought any spindle could have a quick release chuck adapted to it. I hope that some manufacturer sells an adapter that would thread on to the spindle and accept a quick release.
It looks like I will try to build one.
Again like you said, the mechanics may not be too hard to do but being a newbie I am concerned about writing a tool change program.
What I had in mind was a tool station at one end of the table. This needs little mechanical setup and perhaps a lot of programing. I invisioned moving to the table edge, sliding the quick release over the tool holder, dropping it and moving over to grab another tool.
The kicker is that I have 0,0 out in the middle of the table many times. How would I tell x,y where the tool rack is located with 0,0 in different locations?
I think changing 0,0 in the middle of a job, moving to the far end of the table then resetting 0,0 to whrere it was may cause some problems.
Any more thoughts on this?

[thewoodcrafter]

http://home.comcast.net/~jlt313/Router/CNCRouterBuild_files/MOV00482.mpg
Now this would work great.

[myxpykalix]

thats really clever...

[mnrite]

That video is great, anyone have info on where to get that hardware?

Thanks
Mike

[thewoodcrafter]

Here is the company that sells the quick release.
http://www.hightechsystemsllc.com/index_files/Page837.htm
I will be calling them this morning.

[zeykr]

That is interesting - keep us informed about what you find.

[richards]

Roger,
The Taig mill is a mill for cutting metal. As far as I know, its spindle motor runs much slower (top speed around 3,000 RPM) than the spindle on a CNC router. Can it handle 18,000 RPM? Also, it fits an ER-16 collet. ER-16 is much smaller than the collets supplied with the Colombo spindles.

But, it is impressive.

[conceptmachine]

Has anyone tried to make a quickchange collet for the pc router?If anyone has a dead pc router they would like to donate(preferably with a good spindle)i will try to come up with something that works.
Thanks,
Shawn

[thewoodcrafter]

I called the company to order one.
They said max RPM would be 10,000.
He didn't know of any other product like this rated for the higher RPM that we need.
Dead end.
This would have been perfect even without a automatic tool changer. My hands would be the tool changer.

[olecrafty]

Colombo has spindles with tool changers. Try pdscolombo.com they are the Colombo distributers for the U. S. Most brands have a changer available it will take a little more research.

Kaiwa
olecrafty@charter.net (mailto:olecrafty@charter.net)

[myxpykalix]

Shawn, re: quick change collet:
http://www.legacywoodworking.com/products.cfm?product=20
I use this on my porter cable router on my legacy ornamental mill. I know some of the experts say don't use one but i'm going to be getting another for my bot. I've been using one on the legacy for years with no problem and it sure is a whole lot less hassle.

[thewoodcrafter]

Jack,
Does this replace the collet nut and taper?
And does the set screw hold the bit?

[myxpykalix]

yes you stick the bit in, use a long handle hex wrench (you know, the kind with the plastic T handle) give it a little turn and GO! I'm frustrated with the 2 wrench setup cuz my dust hood gets in the way and I can't see how my wrenches go on and they tend to slip so this eliminates all that. Here are a couple pics. Sorry but the size restrictions here won't let me post a decent picture.

6747

6748

[conceptmachine]

Jack,
That's a neat idea but what i had in mind was a collet that you could have a tool set up to a fixed length so you could do tool changes without zeroing the tool each time.Is there anything out there that will do that?
Thanks,
Shawn

[rhfurniture]

Has anyone tried using the shank collars used to hold bearings above the cutter (for template following) to set the distance of cutter insertion?
http://www.wealdentool.com/acatalog/Online_Catalogue_Template_Trim_279.html
I havn't, but don't see why it wouldn't work. It would avoid z zeroing, but not the 2 spanner trick.

HNY
R.

[richards]

Tool balance might be a problem with shaft collars. (The high speeds used by a router/spindle seems to frustrate every easy solution.)

[mnrite]

If one of the machinists out there could make something like the "High Tech Systems" in the video above that could run at 20,000 rpm and chuck into a 1/2" collet, I think there would be a market for it.
I know I would want one!

Thanks
Mike

[conceptmachine]

I could make a collet similar to the high tech system the only concern i see is when you use a set screw to hold the cutter you need a flat on the cutter to screw to.the cutters with a flat are refered to as a weldon shank.the weldon shank carbide tools are available for the metal cutting industry but im not sure about suppliers for wood/plastics like onsrud,does anyone with more knowledge than myself on cutters like onsrud know if they offer weldon shanks?you can grind a flat on the tool yourself but you need a diamond wheel to do so.
shawn

[mnrite]

Shawn,
I would think about a collet similar to "Eliminator Chuck", a set screw is used to close a "C" shaped ring that holds the bit without a flat. That ring would then somehow snap in and out of a quick release chuck.

Mike

[richards]

Has anyone looked at the ISO 30 or HSK63-F toolholders that PDS Colombo specifies for use with their Auto Tool Change spindles? It seems to me that it would be easier to make an adapter that incorporates something that is widely used rather than start from scratch.

[conceptmachine]

Hmmm lots of options here,ill give this some more thaught.What i really need is a pc spindle to experiment with,anybody have any dead pc routers laying around?
shawn

[thewoodcrafter]

I think the set screw is easier and faster then what I have now but I sure would like to find a quick change collet that can handle the RPM.
I looked at the PDS web-site. Not much there, very poor site. I may call them Thursday.
I guess more research. Someone must make something like that.

Shawn, I don't have a dead PC but I do have a dead Craftsman.

[myxpykalix]

Heres a thought...I have no idea of the workability but it came to mind. You may need a higher Z to make this work. You know the connectors that are on the end of an airhose, a female connection that you insert the male connection, like on the end of a nailgun. The outside ring pulls back allowing ballsbearings to slide out and allow the male part to come out of the female part or be inserted. I don't know how tight of a fit there would be to eliminate any wobble but the main concept is a quick release which is what most guys want anyway right? You could make a holder where your tool stands up but as the spindle/router comes over top of it and moves down the holder pushes up the sides of the female connection similar to that link for that video that was posted here for that toolchanger. The female part would be mounted and the male part would have to be on each end of the different tools. Doing that would allow for a hands free release. Just an idea...

[hines]

Anyone ever use one of these? http://www.woodworking.org/WC/GArchive99/8_23powercollet.html
I did a search today on wrenchless chucks and found this. The instructions say it "snaps" to release the bit.

[Brady Watson]

'Quick release chucks' have been discussed on here in the past & the final result was that it was a bad idea when used on a CNC. All of the low cost solutions just cause problems & take away from productivity rather than boosting it. With most routers/spindles you can change tools in under a minute...so one has to ask if a toolchanger is really needed and worth the cost of a 2nd CNC. Few operations warrant the need for an automatic toolchanger. Those who do have enough volume to justify the purchase, don't find the cost is a problem.

-B

[conceptmachine]

I've given the quick release idea some thaught,here's my opinoin.1-the snap on-off method probably wont work well because you need some force to pull the collet into spindle especilay with the high rpm's of the motor,the only solution to that idea would be a draw bar and i dont think that there is enough "meat" on the spindle to drill a clearance hole through the spindle.2-i think that making an adaptor to fit the pc that will accept another tool holder will add to much weight and also would increase tool runout do to the stack-up in the tolerances.3- what i think may work is a tool holder that has a set screw to hold the tool in place so you can pre-set tool height when you have multiple tool changes on a job.and that brings us back to still having to use the spanner wrenches is having a pre-set tool lenght worth the hastle of still using spanner wrenches?what do you guys think?
--shawn

[thewoodcrafter]

A preset tool length would help. Eliminating resetting Z would be great. How are you going to do it?

[richards]

It might be a good idea to visit a shop that has a CNC router with tool changer. If that's not possible, another option would be to visit a machine shop that has a milling machine with tool changer. Sometimes just seeing the tooling is enough to start or stop an idea.

The one thing that I've noticed is that CNC tooling using ISO-30 holders is large and heavy, meaning that securely holding the tool would take a massive ISO-30 spindle. It also means that tool balance is critical - especially when you check the prices to replace bearings in a Colombo spindle.

In my little shop, I do almost all of my cutting with a 3/8-inch cutter. When I have to use something else, the two minutes that it takes to change a cutter is reasonable.

It seems to me, that if your production really needs a tool changer to be efficient, that the basic Shopbot might not be the best machine for the job. If I had contracts that required frequent tool changes and the margin required that an automatic tool changer be used to be competative, I would probably be looking at the $125,000+ machines instead of trying to modify my Alpha.

[jhicks]

We did a time study on the changes to go from 3/8" collet for a 3/8" compression bit for dadoes, then to 10MM shank & collet and bit to drill 5mm holes 1/2" deep we ran on cabinet sides, then back to 3/8" collet for 3/8" compression cut outs.
We originally thought it took too much time for bit changes and considered running dado's and cut out, removeing panels,then reloading and repositioning all the cut out panels for drilling so we would run without bit changeover.
After review, the changeover is far better than repositioning material just to avoid bit change for drilling. Plus you know the parts are in exactly the right spot for critical drilling.
We do not have the dust skirt used on porter cables so ours is always on the material and the spindle travels independently from the skirt so that is perhaps a significant difference BUT, when we had collets and bits ready to change on the bench and didn't have to "look for them" to change, the changeover time to unload, reload, and re Zero the Z averaged 90 seconds.
So when we run a full 4'x8' sheet with multiple sides, backs, or whatever, the time to run a full sheet averaged 2 minutes per panel for dados & cut out, or 10 to 15 minutes per sheet and 60 to 90 seconds to change, reZ and restart over an entire day.
It took longer to clear the table, mark the parts, clean up the dust, position new material, and turn the vacuum hold down back on than to change bits and more time than to cut and dado without holes. Drilling did take longer depending on the number of holes but it usually ran 5 to 15 minutes to drill everything on the sheet.
All dados and cut outs were done in a single pass on prefinished 3/4" veneer ply at 160 IPM with ascension control box on our PRT.
Others run faster but we like this cut speed for full depth and good chips.

Maybe there is a skirt like the old spindle skirt that would be on the material and one wouldn't have to remove the skirt but the overall changeover time is pretty low. Even a tool changer must take 5 to 15 seconds so how much can one save? 30 to 45 seconds?
I'm more concerned about removing, cleaning off dust for good vac holds down and replacing material sheets. Even when we had sheets stacked right at the end of the table at table height to remove and slide on a new one, the average time still exceeded bit change time by as much as 5 or more minutes.
These time studies were done over an entire day where all we ran were sheets and cabinet sides for an entire kitchen so I think they are about as good as we could get as far as averages.

Hope this helps quantify what we found.

[dingwall]

http://www.woodworking.org/WC/GArchive99/8_23powercollet.html

Those add considerable length to the end of the spindle. Any runnout gets magnified. I tried one, followed the instructions, couldn't get it to run with minimal vibration and took it back. Same with the allen wrench style.

[conceptmachine]

Roger,
My plans are to have a collet similar to the pc collet but make it longer and put a precision hole with a set screw to secure the bit.
Shawn

[terryd]

Jerry,
My non-cutting numbers worked out to almost the same as yours give or take 5%. Close enough. What we did was have and entry and exit table at each end. Complete uncut sheets on the left, cut out parts and sprues on the right. Sorted, numbered and cleaned up while cutting the next sheet. We shut off the vacuum valve and hooked up compressed air to the vacuum table and it acted just like my kids air hockey table. The new sheet just slid along and pushed the finished stuff and waste off nice and neat. At the end of the day swept the 6" deep pile of dust into the floor register of the dust collector. Also made two custom box end wrenches that made changing bits and collets a piece of cake.
Shawn, if you plan on using set screws to secure the bit you will have to put flats on the shanks of the bits or the bits will spin and you better buy a large supply of screws because the will be stripped out after a half dozen uses as will the allen keys.

TerryD

[conceptmachine]

Terry,
Yes you are correct about the flats,i stated in a earlier post that this maybe an issue with some cutters especialy router specific cutters.since i work in a machine shop i have acces to diamond grinding wheels so its not an issue for me but maybe a hastle for someone else.there are suppliers like msc,travers tool,j&l etc...that stock carbide endmills with flats on them.as far as the set screws stripping that is more likely caused by overtightening i have some endmill holders that have had the same set screws for over 15 years and they still work good.
shawn

[allegheny]

Don't know if this could be modified for either a spindle or a router, but here is a miniature tool changer that has its own Yahoo group:

http://home.insightbb.com/~joevicar3/default.htm

http://groups.yahoo.com/group/minitoolchanger/

Brian

[thewoodcrafter]

Jerry,
It seems you have put alot of time and thought into this tool changer thing.
I don't have very much time using my Shopbot in a production environment.
But -
It seems to me that it is not just the time to change the bit, 90 sec, it is also the time spent waiting to have to change the bit.
Just looking at from my limited experience, it seems that if you have a job that takes say 30min a sheet to cut and has 3 bit changes that the operater could be doing something else for the 30min. instead of just standing there waiting.
Or said differently, a whole 30min to do something else can be more productive then 3 - 10 min periods.
It just seems way more efficient to have things more automatic.
Am I looking at this wrong?
If my operator can do something else 15 - 20 ft away from the machine, it seem to be better use of time.

[brian_h]

The tool changer on that shurline was spectacular. Thanks for the link, Brian.

Brian H.

[joe]

I just received a very nice note from http://www.hightechsystemsllc.com/index_files/Page837.htm about the maximum RPM.s for there collets. It's 10,000 max.

Nice looking product. When will someone come up with a safe quick change system made to tollerate serious RPM's? We need it. Even at twice the price it would be a bargin.

[benchmark]

Check this out

http://video.google.com/videoplay?docid=-2674911940888627972

[jhicks]

Roger, no doubt there are minutes between cutting, bit changes, cleaning, and reloading.
Certainly if you are in a mode where every minute must be occupied with hands working you are correct. I found that monitoring the parts, and working on other files, or simply moving the scrap out of the shop kept me busy enough between sheets to meet my criteria for being as productive as I thought was reasonable and ready to reload when parts were completed.
I hope you do find ways to keep that busy and make a lot of cash whole while you're doing it.
As most on this forum would agree, what counts is What works for you. New ideas and others experiences here seem to help folks in many ways.
If the bit change over is your largest time variable to focus on and reduce, your process is well tuned and maybe it is time for a tool changer.
I just think of time as money and I don't forsee having the volume to offset 11,000 minutes of change over as break even on a $16,000 tool changer or these type of parts to concern myself with.
I calculate I would need to have a backlog of 133, 40 hour weeks of demand at 30 minutes per sheet/ in cut time to create that kind of bit change over time and then it would be time for more shop bots in here.

[hines]

http://www.cnczone.com/forums/showthread.php?t=28665

Here is the full thread about the ATC that is seen in the google video. Basically, like Joe was saying, it's only made to be used at 10k rpm's max. From what I gather in that thread though is that some of the guys have emailed the manufacturer and they replied saying that they are working on a higher RPM collet.

[thewoodcrafter]

Dave,
I called the manufacturer about this. He said they were NOT working on a higher RPM model and was no help at all.

[hines]

great, oh well.

[sam_harbold]

Just wondering if anyone has tried this unit.

http://www.midwestrapidtool.com/prod01-QuickChangeRouter.htm

From the video it looks like he has it installed on an older PR Shopbot. I would be interested in any comments from anyone who is using or has used this unit.

Sam

[conceptmachine]

Sam,
The concept is a good one but my biggest concern would be the tool holders.If you notice there is no key on the flange that would prevent the tool from slipping in the spindle.The only force is from the drawbar and by the looks of it its small.We all know what will happen to the tool holder and spindle when they slip at high rpm's.....TRASHED.
shawn

[paco]

I haven't tried it...

I like the concept too but I don't like the collet (or the way the tool bit are held in place). I think I could be a buyer if the tool holder would chuck in the router collet instead or this keyed one.

The other limitation I can think of is about the tool length...

[dray]

it would work fine if there were a key and keyway. But then you are adding more moving parts etc

[dingwall]

That's some brilliant work there. I'm not a fan of the PC's taper. If they ever get a Milwaukee version, I'll be in for sure. Even if they don't it's awful tempting.

I wonder how you'd mount an air purge to clean the tapers between tool changes?

[jeff_guinn]

Why do you need a key or keyway on a tool changer? I don't believe any tool changer uses anything but the holder taper & draw bar attached to an air cylinder to hold it securly in the matching collet taper.This is the same principle as the morris tapers used on lathes,drill presses,etc. with the added security of a draw bar.

[richards]

Here's a link to a BT 30 tool holder at http://www.techniksusa.com/metal/thbt3035.htm (http://www.techniksusa.com/metal/thbt3035.htm). In Googling some CNC router tool holders, I couldn't find any with keyways.

[conceptmachine]

Well i could be wrong about the key im just use to them here at my day job on cnc machining centers all of ours have keys although they do lock on the taper the key is there if it did want to slip.Our machines have anywhere from 7 to 30 hp spindles so i guess on a router it may not be needed.I'm still not sure about the modified pc though,after drilling out the shaft to have clearance for the drawbar how thick is the wall? if it's too thin there will be warping issues with heat.just my .02 worth
shawn

[paco]

I think it would be quite a problem to modify the Milwaukee to have a drawbar through as there is the speed controller on top of the armature shaft (http://picasaweb.google.com/the.real.paco/MK5625BearingsReplacement/photo#5037181732818920082). I haven't yet open the PC so I don't know how the drawbar is fitted for the pull cylinder...

I think (kinda of read it) this modified PC is mostly (only) intended for light use. Still it must be really cool!

[sam_harbold]

Apparently they are also working on a system for the Milwaukee router as well. This was taken from there FAQ page.

Question: Is this available with the Milwaukee 3 1/2hp router
Answer: Not yet. This is in the works. Keep checking the web site for updates on the progress.

[3imoh]

Paco-

I was thinking the same thing. I removed the adjustment rod from my Milwaukee router a while back, and remember quite a lot of stuff at the top. Here is something interesting: http://www.jessem.com/motor.htm

I wonder if these guys are using the same tach...they mention something about a "premium tachometer" on the page. Maybe it would be a smaller package at the top since they are also remote mounting the speed control. I dunno... A (relatively) cheap tool changer for that router would be a nice bit of kit, though.

[paco]

I didn't much of it yesterday as I now remember how the 'Electronic Feedback Module' (http://picasaweb.google.com/the.real.paco/MK5625BearingsReplacement/photo#5037180328364613938) is designed; maybe it could be drilled at the top since there only a thin plastic shield and this aluminum support (http://picasaweb.google.com/the.real.paco/MK5625BearingsReplacement/photo#5037181732818920082) to get through. Better yet, they might be considering another 'Electronic Feedback Module'...

[bstern]

I'm a total nube but, after looking at the Midwest rapid tool videos I did a little research and you can purchase a 5 hp tool changer spindle for about 6K from Ekstom-Carlson. This leaves only a tool pallet, air switch and solenoid, and some basic programming to make a complete system. I'm sure I'm missing something.
Is there more to it than meets the eye?

Bob

[harold_weber]

Bob, a few other hardware items you would need are a VFD, tool holders for each router bit you want to have available for changing, and VFD electrical cable to run between the VFD and the spindle. Why don't you do a little more research and get Ekstrom Carlson to come up with a price for EVERYTHING you need for, say, a setup to select 8 different tools. Please let us know what price they quote for the whole setup.

Not only does someone need to work out the programming to change from one tool holder to another, but the VFD itself has a programmable controller in it that needs to be programmed
to run the spindle properly.

[bcammack]

Tool change programming can be done as a subroutine. The drawbar action can be handled with the S# commands and the tool presence can be handled with the Input command.

I'm guessing $12k worth of hardware based on what Bob and Harold have posted. What you pay for in the turn-key package is the skull sweat that somebody invested in making it all play nice together.

[bstern]

Hi Brett,
I guess I am missing about $4000 in costs.
Lets say about $800 for a VFD.
How much for the tool holders. ($100?)
Tool Palette can be built for say $250.
Couple of relays.
I only see about $1500 to 2500 in additional parts for a 5 tool system.
Looks like it could be done for under $8500.
Am I missing something big?

The bot programming seems very basic at first look.
The spindle programing is something I know nothing about.

I need to start cutting with the one Z I have and then I want to look at this closely.

Sweat equity is not a bad thing in that I would understand the tool much better than if I purchased it. ($7500 is a lot of equity)

[bcammack]

No. You may not have. I did that off the top of my head without further research and a healthy respect for how things generally more expensive than they appear at first blush.

One thing about the tool changes on our Omags and Northwood mills, the spindle orients itself, rotationally, to a particular point before performing a tool change. I presume there's a sensor for that on the spindle under discussion. This sort of thing would require a more intimate interface between the ShopBot controller box and the VFD to rotate the spindle slowly until a sensor fired off to indicate "home".

I'm just blue-skying at this point about it, but from the perspective of a computer geek with 30 years in the business and several detours into machining, fabrication, and, recently, into CAD, CAM, and CNC.

[bstern]

Brett, Thanks for your prospective.

I am not experienced at all on the machining part.
That's why I was asking if I was missing anything big. From what I have seen on the tool change spindles with ISO tool holders there does not seem to be a need to rotationally orient.

What I was looking for here was anything big that might scare me away from further research.

So far, as time permits I will continue and report back on what I find.

[innovative_cabinetry]

Does shopbot have a tool changer upgrade that works? I would lean towards a shopbot if that was the case and if it was in the ballpark pricewise. I was quoted a CNC from shopsabre and the difference in price between a 4hp HSD spindle and the 5 hp HSD with the ATC is $7,000. Not inexpensive, but not necessarily out of line when you consider what you get in time savings from not having to switch out bits manually.

[ed_lang]

I saw the tool changer in operation at the Jamboree last year when it was held in Durham, NC.
I must say that I found myself standing watching and dreaming.

If I recall right, the changer had 8 tools to pick from.

[bstern]

The current price of the ShopBot tool changer is $16,000. It seems that techno and shopsabre are both about $9K on its own. I wonder why ShopBot is so high. I heard that they are trying to get it down to $12K. Even that seems a bit high. At $16K I am considering building my own. At $10K I would purchase from Shopbot.

[bcammack]

I think the price is what it is because of the factors I described. There are research, engineering, and support costs that go beyond the simple cost of parts and they have to be amortized over the product life by the sales, plus some sort of profit as well.

A tool changer at this machine's price-point is going to be a niche product without the sales volume necessary to amortize the intrinsic costs in smaller increments. There's probably $9k just in pieces to put it together and raw material prices for steel and copper are just going through the roof these days.

[innovative_cabinetry]

I hear what you are saying Brett, but to me if Shop Sabre can put one together for 10,300 for the whole package,including the spindle, then it would seem that shopbot should be able to get it done for a similar price. The SS is a 5 tool changer instead of 8 and that may account for some of the cost, but still.

With that 10,300 you also get a 5 hp spindle included in the price which, when taken into account makes the price much easier to swallow.

[elcruisr]

One thing to remember is the additional cost of running a tool changer setup. Tool holders are not cheap and they do wear out and have to be replaced periodically. You have a large increase in the price of the spindle. You need to supply it with very clean and dry air.

I've been cutting cabinet and furniture parts for 6 years now and if you learn the programming tricks and sometimes make a few modifications there isn't always a good payback on the investment. For some there is and then you might want to be looking at more of a mid range machine anyways. I know shops with the two other machines you've mentioned and their performance has not always left everyone happy although there are those that are.

Tool changes are not as big a deal as many think. I can change a tool in under a minute. It takes a lot of changes to pay for the extra cost for me.

If you can handle the programming it's not so terribly hard to write a subroutine to run a tool changer if you have the spindle. It's just not worth the hassle to me in my operation to bother with though!

[ryan_slaback]

Eric,
I agree that the actual change time is not that great. i.e. less than a minute But for me anyway it always becomes much more time than that as it usually goes more like this.

1. Notice machine has stopped and bit needs changed (approximately 30 seconds)

2. Get to a good stopping point in what I am currently doing to go change bit (30 seconds to 5 minutes)

3. Go into control room and jog machine to end of table. (30 seconds)

4. Change bit (1 minute)

5. Go into control room and jog tool back onto material (30 seconds)

6. Run Z Zero command (30 seconds)

7. Put away Zero plate (15 seconds)

8. Find and run next file (15 seconds)

9. Walk back across shop to whatever I was doing. (10 seconds)

If there was a changer with preset variables for Z depth I would not have to even notice.