8" or 16" Z ?

[dubliner]

Well I think I've narrowed my new 'Bot down. Now my dilemma is whether I should get the extended Z as I would eventually like to get an indexer. I will not be making a table so "inletting" the indexer is not an option for me. In that case do you give up surface area & what are the pros & cons of that? I'm probably getting the 120x60. TIA Neville ~ See you all in San Mateo :-)

[minnlaker]

Neville, you and I are both trying to make the same decision. I have questions about the new PRS model which I will need answered before I can decide. I am working with Diane from Shopbot.
My biggest concern is adding the indexer along side the "X" rail.

[wayneo]

Hi Chuck/Neville,
I have a PRT-96 Alpha and Indexer. I initially mounted my indexer along the C-channels (X-axis). I have a 12" Z-axis.

I am going to remove it(the indexer) from the side and place it flat down on the cross angle pieces. I don't like it on the side (C-channels).

To accomodate the Indexer, I sliced off about a foot of a raised bed that I made on my table. Made the whole thing so I can easily replace this one foot piece if I need, or use indexer. Either is very easily installed on the bed.

Why did I make a raised bed? Well, cutting is more accurate if the Z is only extended a short amount, like 4-6 inches. At 12 inches, it is not as accurate since it has a 12" lever arm acting against it.

If I need to cut a really big piece, like 4'x8'x12", then it is also easy to remove my raised bed and replace with a sheet to cut on.

I really did not want to cut the steel angle pieces to make a dropped bed area for the indexer. I think my way gives me the most easily reconfigurable machine without sacrificing the strength of the steel table.

By going with the 12" Z-axis option and the steel table, they simply added a couple C-channels under the initial one so now I have 2 C-channels along the X-axis. Makes for a real stout table, albiet a little on the heavy side!

Good Luck!

Wayneo

[jamesgilliam]

Neville/Chuck, All I can add is what I ask myself on the 48x96 or 60x120 inch table, Why didn't I go for the larger one? If Wayne would post a picture of his raised bed bot it would give you a reference point to go from. While 16" seems a bit much, the first time you need to work with something that will not work under the 8" height you may kick yourself. Next time I am in Durham I am going to check into raising my Z a few inches. James

[dubliner]

James et al, Yes the raised table sounds very interesting, seems like it would aid rigidity when pushing through hardwoods, provided it wouldn't be a pain to convert back & forth. What do you think are the issues of flexing with a 16"Z at full extension?

[wayneo]

Hi Guys,
I will try to take some pictures tonight after work and post them. Was going to do it last night, but too many other things running interfearance....

Regards,

Wayneo

[hespj]

I've got an indexer and 12" Z. I made a raised bed (isn't that something to do with gardening?) to reduce Z axis flex, which was as much as 1/16" in the X direction. My raised bed is simply a box with 4x2" sides and cross members, with MDF top and bottom. Not to difficult to remove if need be.

[jamesgilliam]

Neville, Had not thought of the flexing issue. I would think that would be minimized by a heavier Z axis to get the 16". Material and cutting speeds could influence it also, and tooling choice. James

[minnlaker]

I am going to throw a wild question out onto the forum. Has any loyal customer of shopbot been asked to field test the new Apha PRS. If so can you answer the flex question above for the new Z axis with a 16" plunge. The questions Neville and I have are about the new PRS. I sense our questions may need to be directed to Shopbot if they are the only ones with experiance with the new PRS models.

[hespj]

I should add that I built a box to reduce the Z height as a result of flexing on the Z axis of a Alpha purchased 2 years ago. I recently bought a second Z axis, and this has twice as many bearings, which I think should reduce flex by giving better support. Oddly, the original Z axis has mounting holes for these extra bearings, but no bearings.

Another thing worth bearing in mind - it seems to me the flex issue increases dramatically with length. Obviously the more Z axis protruding below the carraige, the more flex. But also, the longer a Z axis, the further it is between the bearings, and there seems to be some flex between bearings. So the problem is compounded.

[wayneo]

Hi Guys,
OK, well here are the pictures (I hope) that I promised some days ago.... Sorry for the delay. Too many things going on this time of year!


6735

My raised bed is made out of 2x4's spaced 11 3/4" on center, one sheet of 3/4" Birch Ply screwed to the 2x4's, two sheets of particle board on top of the birch.

I then cut off one foot for the area where the indexer is mounted. This one foot x 8 foot piece is easily mounted (after removing the indexer) or removed (for using the indexer). Whenever I flatten my table, I remove the indexer and put the one foot removable section back in place. That way everything stays pretty much the same.

Note: I plan to remove the indexer from its present sideways mounting to the C-Channels and mount it flat on the angle iron cross pieces. I need to make a piece of T-Slot channel to do this. I plan to make the T-Slot about 10' so I can do a full length 8' turning. I will mount the T-Slot to the Angle Cross pieces so that the removable one foot section of the raised bed can be installed stradeling the T-Slot. Then you only have to remove the Indexer head and tail stock pieces. Having the T-Slot mounted permanently this way ensures that it will always be aligned properly.


6736

Next picture below shows how the 2x4's are fastened to the Angle Iron bed supports. Lag screws and double fender washers were used so that holes did not need to be drilled. This allows bed to be shifted as needed.


6737

I also added E-Chain cable ways to better manage the control cables and keep them separate from the dust collector hose and power cables.


6738

This shows the cableways for the X-Axis. Note: I made sheetmetal trays to hold the E-Chains.


6739

I hope this makes some sense. I find it very flexible and retains the full strength of the Steel Table. I believe putting a dog leg in the cross angle pieces create a weak point that would allow flexing where you really don't want any. Using the raised bed means it shortens the lever arm of the extended Z-axis to approximately 6" or so.

Good Luck!

Wayneo

[dubliner]

Wayne, thanks very much for taking the time to do that. I've seen a few machines that were converted to E-chains. My first impression is I prefer it to the boom. Was it much to modify yours for the chain? I will digest all the other info you posted in the mean time, tx ~ Happy New Year all

[fleinbach]

Neville,

Putting on the echain is not very difficult. Here is a link to a previous post with more information about it. There are many more but this was recent. Just do a search for "chain"

http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=42502#POST42502

[wayneo]

Hi Neville,

Well, adding the e-chain was pretty simple. Hardest part was coming up with a tray to support it. After fiddling around with it and thinking about it, I had a sheetmetal shop bend me up some trays out of galvanized steel sheeting. I screwed them onto the Y cross piece and along the X axis using self drilling/threading cap screws.

Main reason for doing this is I had everything fastened to the "Bow Thingy" and it just seemed to be too much for it. Also I was reading where other folks were having quite a time with control signal problems caused by Static Electricity generated by the close proximity of the dust collector chute and possibly by the power cables being close to the control cables.

I continue to use the "Bow Thingy" to support the Dust Chute and the Power Cable to the router. I put all of the other cables (control for the stepper motors and Zero Plate/Probe cables) in the E-chain. It dresses down nicely and just looks more professional......... Sorry, I am an engineer and like to have things look nice as well as being functional!

Here in Alaska it is real hard to get some materials, like Trupan or stuff to make a vacuum bleeder board with. In talking with the folks at AllStar Adhesives, they suggested using a sheet product called Azek for the table. According to them, it lays flat and stays flat. The particle board is subject to adsorbing moisture from the air causing it to swell or buckle a little. I plan to special order some of this material and try it next time around. Particle board is not very smooth once you flatten it. Then using double sided tape to secure stuff kinda pulls particles out of the particle board when removing the tape.


I am tempted to try cutting my T-Slot material out of aluminum, but not real sure I want to deal with the mess or take a chance on screwing it up. Not exactly sure where you can get this stuff without it costing an arm and a leg.......... It sure would make for a sweet setup though, to have a T-Slot that went along the X-axis and then the removable raised bed section could straddle the T-Slot.

If anyone knows where to get the T-Slot material ready made or where to have it cut, please speak up! I am thinking reasonable price here. Would like some about 10' in length. That way I could mount the Indexer head and tail stock on the T-Slot beyond my 8' table. I will have to make some riser blocks out of aluminum to mount under the head stock and tail stock. That way I should have about a 14" diameter on the Indexer for turning.

Just some thoughts for your consideration. I remember what it was like when I was trying to decide how I wanted my machine configured before ordering it......... Just part of the fun!


Regards,

Wayneo

[fleinbach]

Wayne,

I'm not sure if you have the same Echain as I do or not. Mine is from Ingus. I did not need a tray to hold the chain up. I don't recall the exact distance, but the Echain is self-supporting up to a point. All I did was add a a long bolt about 16 inches from the pivot point of the chain. The chain stays pretty much up in the air past that point for several feet all the way to the end of the X and Y car.

http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=42502#POST42502

[myxpykalix]

Wayne,
talk to scott cox about the t-slot in aluminum deal. From what he told me it was an an ordeal and an expensive one at that. Maybe he'll speak up here...

[scottcox]

Wayne,

Before I started, I asked for quotes from local machine shops and got an average quote of $700 to mill just the slot, not the recessed bolt holes (that's in MY material).

Being the stubborn, cheapskate, do-it-yourselfer that I am, I chose to do it myself. And I knew the 'bot could do it. I just had to learn how!

So... I paid about $300 for the 6061 alum. bar stock (1.25in x 6in x 12ft), then another $50 for the .25 straight bits, then $125 for the t-slot cutter. It was a royal pain in the ahh, wallet, but well worth it.

I think that there are different sizes of t-track for the different models of indexers, so check carefully before buying the stock.

Let me know if you have specific questions.

Scott


6740

[wayneo]

Hi Scott,
Thanks for the info and picture.

Yes! I am sure it was an ordeal! Did you machine it dry (no lubricant)? Exactly what aluminum plate did you use? 6061-T6 or other?

Did you use a dust/chip collector or just let em fly? What kind of bit did you use? Speed/feed? Step over/step down? How did you hold it down while machining?

My son-in-law is a journeyman machinist.... Maybe I can get some inside info......???

I have been thinking that there should be some kind of ready made stock that could be ordered from someplace.... Just don't know where. Have also been thinking that it might be possible to assemble one out of common bar stock and flat plate, but not sure what is available. I don't think super accuracy is necessary. Just within a few thousands.

Have you done much with your indexer? There seems to be a very serious lack of documentation about how to do anything other than fancy cylindrical turnings or fluted columns. I am especially interested in how to wrap reliefs around non-cylindrical shapes (sort-of-like Coke Bottle shapes).

If anyone has any info or documentation, please speak up!

Regards,

Wayneo

[scottcox]

Wayne,

I used WD-40 for lube and compressed air to cool the bit and evacuate the chips. I tried it dry and things didn't go so well. I found it was faster and cut better using a lube. But it was messy!

For the main slot I used 18K at 1ips with .0625 stepdown and .0625 step over. I've read about other going faster and deeper, but after ruining 3 bits, I stuck with what was working for ME.

The T-slot cutter was a different animal. With the main slot cut, and the t-slot cutter installed, I set the RPMs at 5K and the move speed to the lowest possible setting (0.05 ips) and had my brother just bump the arrow key as I cut one side of the "T", constantly lubing and cooling it. Hold it too long and the 5hp spindle bogs, so it was slooooow. Didn't want to let the smoke out of that spindle!

I held it with clamps and through bolts. And because it was 12 ft long and I did it on my 10ft table, I had to do it twice.

You can see some other details and suggestions here in this thread....

http://www.talkshopbot.com/forum/messages/312/14964.html?1166759145