T-track/vacuum hold down

[Keith Larrett]

When I first made my spoil board I figured that I would eventually need/want a different design. After nearly a year of using the ShopBot I think I know what I want, but I'd like to get some advice before I start buying the parts.

I have the 16.9hp regenerative blower from ShopBot. It works great for most of what I do, cutting cabinet parts from sheet goods. However, I'd like to start using the machine to cut other cabinet parts, namely fluted fillers, appliques etc. So I'd like to have another hold down method.

I was thinking of putting t-track into the spoil board along the x-axis at 6" centers. That would give me the option of clamping hold down. Then when I needed to cut sheet goods I would put a temporary 1/4" MDF spoil board on the bed and use the vacuum to hold down the sheet goods.

Is my thinking sound on this? Any thoughts/comments on how practical this would be? Thanks in advance.

[Keith Larrett]

On a side note. I edited my signature with the details of my machine, but my signature is not showing. No idea why not :confused:

Edit: Ok. There it is. I guess it is not "retroactive". Only shows up on new posts.

[jerry_stanek]

What I do is I have a 4X8 PVC sheet that I cut tracks into and throw that on my vac table and use the vac to hold it in place

[Gary Campbell]

Keith...
Jerry's method works, but requires the vac to run.

Installing T Tracks into a vac spoilboard allows the t tracks to reduce (eliminate) vacuum near them. Here is a screen shot from my Vac & Hold Down class that shows the reduction: (Higher the blue arc, lower the vacuum available)

http://www.talkshopbot.com/forum/attachment.php?attachmentid=26746&stc=1

[Keith Larrett]

What I do is I have a 4X8 PVC sheet that I cut tracks into and throw that on my vac table and use the vac to hold it in place

Jerry. I was wondering why you used PVC instead of say MDF or Plywood. Is it because of the weight or the stability of the PVC? Thanks.

[Keith Larrett]

Installing T Tracks into a vac spoilboard allows the t tracks to reduce (eliminate) vacuum near them. Here is a screen shot from my Vac & Hold Down class that shows the reduction: (Higher the blue arc, lower the vacuum available)


Thanks Gary. I didn't take that into account. That looks like quite a significant loss of vacuum.

[jerry_stanek]

I had it and it stays flat after i surfaced it

[Keith Larrett]

I had it and it stays flat after i surfaced it

Thanks. Yes, often it's a case of "I had it on hand". Good to know about it staying flat, something I need to think of with the humidity in Florida.

[gbradley]

Keith

We have done several vac tables for Shopbot machines and we have several different methods of holding small/narrow parts with vacuum. You can contact me if you like at gbradley@allstaradhesives.com

[jerry_stanek]

I also use dedicated vac pucks that I use 1 zone to hold and my compressor for the puck

[Keith Larrett]

Keith

We have done several vac tables for Shopbot machines and we have several different methods of holding small/narrow parts with vacuum. You can contact me if you like at gbradley@allstaradhesives.com

Thanks. I sent you an email.

[bleeth]

Keith:

Like you I do mostly box parts but do cutting on some smaller parts that won't hold properly with vac.
Since my spoilboard is trimmed to x and y zero I just screw down 2" temporary fence at both axes and then after I put the object to it screw down cam clamps as necessary. The small screw holes that accumulate over time are a non issue since by the time there are getting to be quite a few of them it's generally time for a new spoilboard. My vac plenum has a 1" border all around the outside as well as 1 1/2" between each zone (I have 8 zones on a 4896) and will always shoot to have the screw holes over those areas. Not very techie but it has worked well for 10 years plus. If I wanted a t-track table I would likely do something similar to Jerry's but use a piece of 3/4mdf with both sides laminated with HPL, edgebanded, and seal the track dados before putting in the tracks. That would stay flat as long as it is stored flat and could then be screwed or clamped to the table eliminating running the vacuum. Alternately screwed down pucks and my vac table pump would also work great if I had a lot of small parts to cut. For the occasional weird part like a casing arch I just screw it down and use a last pass skin strategy so there is no stress to speak of when cutting through and have never had a part jump.

[Keith Larrett]

If I wanted a t-track table I would likely do something similar to Jerry's but use a piece of 3/4mdf with both sides laminated with HPL, edgebanded, and seal the track dados before putting in the tracks. That would stay flat as long as it is stored flat and could then be screwed or clamped to the table eliminating running the vacuum. Alternately screwed down pucks and my vac table pump would also work great if I had a lot of small parts to cut. For the occasional weird part like a casing arch I just screw it down and use a last pass skin strategy so there is no stress to speak of when cutting through and have never had a part jump.

Thanks for the input Dave! I was hoping to hear from someone doing cabinetry. I'm going to order my t-track this evening, Peachtree has a good Cyber Monday sale going on, but after reading your comments, along with those of Jerry and Gary, I will probably rethink my strategy. I'll probably make up a MDF sheet as you suggest and put the t-track in that. Can't say it will be fun throwing that on and off the table, but in reality it will probably be used once for every ten times I use the vacuum. I will also look into smaller vacuum pods with gasket. I have a vacuum pump that I use on my lathe which I'm sure will work with that.

Thanks again. I appreciate the advice I get here!

[Keith Larrett]

I finally found the time to complete my t-track hold downs. I made four different hold downs. Two 2' x 2' and one 2' x 4'. I put threaded inserts into the spoilboard too screw them down with. The threaded inerts are actually pretty deep, they are in the base board below the vacuum plenum.

Either the 2' x 2' or the 2' x 4' can be placed at 0,0.

I plan on also adding inserts to the left, so the 2' x 4' can be placed to the right of the two 2' x 2'. That way I can have a 2' x 2' area for small stuff, a 2' x 4' for medium stuff, a 2' x 8' area for long stuff and a 4' x 4' area for wide stuff.

I used the heavy duty t-track which is 5/8" deep and takes 3/8" bolts. In order to have some meat to screw the t-track into the slots I laminated two sheets of 3/4" mdf together.

[bleeth]

Looks great Keith. Make sure you store them flat!

[dlcw]

When I first made my spoil board I figured that I would eventually need/want a different design. After nearly a year of using the ShopBot I think I know what I want, but I'd like to get some advice before I start buying the parts.

I have the 16.9hp regenerative blower from ShopBot. It works great for most of what I do, cutting cabinet parts from sheet goods. However, I'd like to start using the machine to cut other cabinet parts, namely fluted fillers, appliques etc. So I'd like to have another hold down method.

I was thinking of putting t-track into the spoil board along the x-axis at 6" centers. That would give me the option of clamping hold down. Then when I needed to cut sheet goods I would put a temporary 1/4" MDF spoil board on the bed and use the vacuum to hold down the sheet goods.

Is my thinking sound on this? Any thoughts/comments on how practical this would be? Thanks in advance.


Here's what I came up with for my shop. It's a piece of 1" MDO with T-track slots. I made 2 4x4 sections to hold blanks up to 8' long. They are held down by the vacuum hold down system. When done, move them to a storage area and the surface of my spoilboard is unaffected.

http://www.talkshopbot.com/forum/attachment.php?attachmentid=27336&stc=1

[Keith Larrett]

I used my t-track hold down yesterday to cut out some curved rails. It went well and I'm excited about the possibilities this is going to open up.

Not having much experience cutting solid wood on the CNC, I'd be interested to know about your cutting strategy. I used a 1/4" spiral down cut bit at 12000rpm and 120 ipm. I think the attached screen shots show the rest of the strategy. Tabs, 1/4" deep climb cut with a final pass in the opposite direction, ramped into the cut. I found it important to put tabs on all four sides of the piece. I may have gone a bit overboard with the tabs, as I had one piece move when I only had tabs on two sides of the piece.

As I said, from my observations it seemed to go smoothly, but i don't know if I was cutting to aggressively or not and I'm sure there are plenty othher strategies I could use to tweak things further.

Thanks for any input/advice.

[Keith Larrett]

Here's what I came up with for my shop. It's a piece of 1" MDO with T-track slots. I made 2 4x4 sections to hold blanks up to 8' long. They are held down by the vacuum hold down system. When done, move them to a storage area and the surface of my spoilboard is unaffected.


Thanks Don. It looks like you are cutting into the MDO with through cuts, so I assume your t-tracks are not flush with the surface?

[jTr]

... I'd be interested to know about your cutting strategy.

You're pretty much there with your methodology, but a couple suggestions that may help improve results a pinch:

- I've been fine at 3 ipm = ok to bump move speed in my opinion.

- You are correct to go with a last pass. I've noted improvement on acute angle cleanliness by running first climb passes .016 to .030 oversize offset. Conventional last pass seems to aid in cleaning tear out.

- I strongly urge you to try a chip breaker style bit for cutting solids. It has serrated edges that help grind chips in the kerf, and seems to greatly reduce solid wood's tendency to splinter. Some light lines are visible from the serrations, but you were going to sand that edge anyway, right?

- FWIW: Last pieces I cut, forgot to add tabs (!) Down cut chip breaker packed kerf so tightly, the pieces came out as if I had tabs there the whole time. (But I have no intent of consciously neglecting them in the future...!)

Good luck - looks like you're well on your way. Now your turn to share some completed project pics!

Jeff

[Burkhardt]

Interesting thread!
FWIW, my problem was the reverse. I have a full surface t-slot table (from 80/20 brand extrusions) and used to bolt my vac pods onto that table. That worked O.K., but the pod surface was not as parallel to the table and it had to be bolted down hard to avoid slipping on the slick anodized table surface. It also made disposable cut-to-shape pods more difficult than necessary.

Lately I modified the table to actually use the T-slots as vacuum line. I plugged the end openings and connected the vacuum hoses to the plug strip. Now I have 6 separately controlled vacuum sections and can put simple pods anywhere on the table. I have standard size 4x4" or 4x12" pods and can cut custom pods to shape quickly from scrap lumber (see pics). The open sections of the active t-slots are covered with thin aluminum flashing that is held and sealed with electrical tape. The pods have 2 dowels that locate the y-direction in the slot while there is an end stop for the x-direction. Minor disadvantage it gets a little more difficult to fish bits and other stuff out when they fall into the slots.

https://lh4.googleusercontent.com/-wiI6opoE_hE/VsjGBuFUoSI/AAAAAAAAGI8/_MFQy3Liztc/w646-h835-no/2-DSC00316.JPG

https://lh3.googleusercontent.com/-Dyrn30FT5YU/VsjGCNVBCWI/AAAAAAAAGJA/J0ie43kJzjQ/w426-h834-no/3-DSC00317.JPG https://lh6.googleusercontent.com/-_CwILkUPWik/VsjGCiJfZEI/AAAAAAAAGJE/YqFXAaCY-Zc/w406-h835-no/4-DSC00318.JPG

https://lh5.googleusercontent.com/-E_ZIHd2Fl2Y/VsjGCy3PzCI/AAAAAAAAGJI/wTZDvvAk_oI/w1024-h644-no/5-DSC00320.JPG

[Keith Larrett]

Thank you for the reply and advice Jeff.



- I've been fine at 3 ipm = ok to bump move speed in my opinion.


I'll try bumping the speed up a bit. I assume you mean 3 ips.




- I strongly urge you to try a chip breaker style bit for cutting solids. It has serrated edges that help grind chips in the kerf, and seems to greatly reduce solid wood's tendency to splinter. Some light lines are visible from the serrations, but you were going to sand that edge anyway, right?



Are these the bits you are referring to? http://www.toolstoday.com/p-5640-cnc-solid-carbide-spiral-flute-roughingfinisher-down-cut-router-bits-with-chipbreaker.aspx?&variantids=6432,0&keywords=46236

I'm sure you feel they are worth the extra cost. Do you know if they are available in smaller diameter? I could only find 1/2" diameter. Upcut or downcut - which works best? I would guess the downcut.


Now your turn to share some completed project pics!

Jeff

I've attached a couple pictures. The wall unit is a project I delivered last week. The fluted fillers I cut yesterday for my current project.

[Keith Larrett]

I have standard size 4x4" or 4x12" pods and can cut custom pods to shape quickly from scrap lumber (see pics).



What are you using for gasket material? I've looked at the offerings on All Star Adhesives site and there is a lot to choose from. Not sure where to start. Thank you.

[jTr]

This is the bit I've been using:http://www.bamcarbide.com/1shx1cutdix25.html

The bit I received does not have the excessive amount of serrations shown on the webpage - see photo below. It's more like one serration every 1/4" , then offset on the second flute, which I feel is better - just enough to break chips down but leave only a few trace bumps from the serrations.

27363


I've had good luck with bits from this supplier, but Centurion tools is my favorite source. Incredibly sharp and great value, as many others here will attest, but they do not offer chip breakers. Ultimately, the good news is it is no great financial burden to get into the chip breaker and enjoy less spoiled parts due to excessive chipping and tear out.

Nicely done on the bookcase! Did you make the divided light doors?

Jeff

[jTr]

One more interjection - gasket material - my favorite source:
http://www.veneersupplies.com/products/Vacuum-Gasket-Tape-For-Clamping-38-x-18.html

Scroll through and you'll find 1/4, 1/8 and 1/16" thickness to cover about any application you need it for. These people are quite possibly the most congenial retailers for woodworkers on line.

jeff

[Burkhardt]

It is this one from Home Depot (http://www.homedepot.com/p/Frost-King-E-O-3-8-in-x-3-16-in-17-ft-Grey-Vinyl-Foam-Weather-Seal-Self-Stick-Tape-V443H/100205904). McMasterCarr has similar material (http://www.mcmaster.com/#catalog/122/3607/=11810gb).

This closed cell vinyl foam conforms to uneven surfaces and compresses under vacuum to about 20/1000". You can rip it by hand, let it overlap on corners because it is so soft and the bit can cut into it without wrapping. It is cheap, recovers many times and works well for me. That said, it can be used only for surface application. If you want to make a pod with a gasket groove it would probably be too soft. For that purpose I carve an undercut groove with a ball end bit and use a foam o-ring cord.

I have not tried the Allstar gasket yet. Supposed to be good but so far no reason to use something else.

[Keith Larrett]

It is this one from Home Depot (http://www.homedepot.com/p/Frost-King-E-O-3-8-in-x-3-16-in-17-ft-Grey-Vinyl-Foam-Weather-Seal-Self-Stick-Tape-V443H/100205904). McMasterCarr has similar material (http://www.mcmaster.com/#catalog/122/3607/=11810gb).

This closed cell vinyl foam conforms to uneven surfaces and compresses under vacuum to about 20/1000". You can rip it by hand, let it overlap on corners because it is so soft and the bit can cut into it without wrapping. It is cheap, recovers many times and works well for me. That said, it can be used only for surface application. If you want to make a pod with a gasket groove it would probably be too soft. For that purpose I carve an undercut groove with a ball end bit and use a foam o-ring cord.

I have not tried the Allstar gasket yet. Supposed to be good but so far no reason to use something else.

I thought that was weather seal. Good to know. As cheap and easy to get as it is, it will be good to experiment with. Thanks.

[Keith Larrett]

This is the bit I've been using:http://www.bamcarbide.com/1shx1cutdix25.html

Thanks for the link. I shall order one and give it a try.


Nicely done on the bookcase! Did you make the divided light doors?



Thank you. No, I didn't make the doors. I'm a one man shop and came to the decision that it made sense to outsource the doors.


One more interjection - gasket material - my favorite source:
http://www.veneersupplies.com/produc...g-38-x-18.html

Great! I'm familiar with Joe Woodworker :) Ordered a number of times from him and have always been pleased with the service and product. Given that you brought him up, do you have a vacuum press and if so how is it set up? I've been wanting to use the vacuum on my CNC for a vacuum press and am trying to figure out how to go about it and what I need to get.

[jTr]

...do you have a vacuum press and if so how is it set up? I've been wanting to use the vacuum on my CNC for a vacuum press and am trying to figure out how to go about it and what I need to get..

Before I found JWW, only option I could find is Vacupress. Bought the all air (venturi) automatic head for around $700. Been working for 12 years now, so very happy with investment. Once project is set in the press, it auto-cycles to maintain proper pressure.

I normally just put a bag on a 4x8 table for pressing. Made a full frame style once, which was easier and worked reasonably well but I had used polyurethane stock for the membrane, and it developed a leak. Important note regarding polyurethane bags- I know their touted as indestructible, but I had a problem with pinhole leaks cropping up after a year of use. Joe caught my review indicating this, and he actually warranted/ sent a replacement. The culprit: florescent lights - supposedly prematurely oxidizes the polyurethane causing pinholes -very hard to detect. Since then, that bag stays rolled up in original carton every second it's not in use. I have not had the occasion to rebuild another frame in part for this reason, but if I do, I'll use the regular vinyl, as I still have original vinyl bag the press came with - only has a couple patches after all these years.

All of Joe's glues are excellent. For bent lamination, I'll use his "ultra-cat" which is essentially a plastic resin glue and forms a rigid glue line. Their standard glues all work well for most any other application, and I love the reduced press time.

As to the Shopbot- I've eyed that table as the ultimate flat surface for pressing, but have stuck with the other table out of habit. One thing I did consider was tapping the vac source on the bot for quick evacuation, but found my festool vac does this very well. Quickly swap to auto vac system once the excess air is pulled out and get those panels and veneers hugging each other much quicker, which is critical for good bonding by reducing open time in this fashion. As to utilizing the vac table source- it's a high - volume low pressure system (mine tops out at about 7" at my altitude.). For proper veneer pressing, you need to sustain 18-22" for entire clamping time of 1 - 4 hours depending on glue selection, so the question of using the shopbot vac system for pressing veneer would be an emphatic "no".



Jeff

[Keith Larrett]

As to utilizing the vac table source- it's a high - volume low pressure system (mine tops out at about 7" at my altitude.). For proper veneer pressing, you need to sustain 18-22" for entire clamping time of 1 - 4 hours depending on glue selection, so the question of using the shopbot vac system for pressing veneer would be an emphatic "no".

Interesting. Yes, that's what I was hoping to do. I've read a number of people doing it on Woodweb. My gauge tops out around 9". I assumed that was because the spoil board was inherently full of leaks. Oh well, it looks like I will have to keep saving for a vacuum pump from JWW. Thanks again for sharing your knowledge and experience Jeff.

[jTr]

I've read a number of people doing it on Woodweb.

Okay- I just had to look that up. Very concerned about the lower pressure as the numbers you and I generate are really alarmingly low based on my education with veneering. However, maybe for a simple flat panel it's worth trying at least once...?

You first!:p

Jeff

[dlcw]

That is correct. I went with 1" thick MDO so the tracks could be recessed about 3/16" below the surface enabling me to make clean cuts thru material without hitting the track.