8 Foot linear guide system?

[jkpugh]

Hi, I am building a CNC drill table for large panels. Travel is 6ft in x and y. So I need 7+ ft of linear guideway, any suggestions? The only torque will be from pushing up on from the drill, 3/8" holes max. Thanks, Jeff

[Switcher]

Rack & Pinion.



http://www.mcmaster.com/ctlg/DisplCt...MainWidth=1068



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[ViperTX]

Well without knowing what precision you need and not seeing any technical specifications on the rack & pinion....I would say you need to do some homework.

Personally if cost is a consideration....then I would use the Wisecarver V wheels and drive the table with ?? Here is where we need to know the desired precision (accuracy and repeatability).

[RICHARD ZASTROW]

'splain "torque pushing up on drill". Does this refer to force pushing drill down or force pushing table up or???? Just to clear up my understanding. I always consider torque to be a twisting force.

[Switcher]

Originally Posted by ViperTX Well without knowing what precision you need and not seeing any technical specifications on the rack & pinion....I would say you need to do some homework. Personally if cost is a consideration....then I would use the Wisecarver V wheels and drive the table with ?? Here is where we need to know the desired precision (accuracy and repeatability).

If your referring to the link i posted, how much more info do you really need?

http://www.mcmaster.com/ctlg/DisplCt...MainWidth=1068





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[ViperTX]

jkpugh...you need to know how much backlash you can live with...then you need to figure a way to preload the pinion to the rack to reduce the backlash....the backlash will determine to a big extent the accuracy of you table.

You could also just just the rack and pinion as a guide...where the rack is mounted to the frame and the pinion is attached to the table in a non-driven configuration.

In that case you would need to use an ACME screw, a ballscrew, or some other type of drive.

[jkpugh]

Originally Posted by ViperTX jkpugh...you need to know how much backlash you can live with...then you need to figure a way to preload the pinion to the rack to reduce the backlash....the backlash will determine to a big extent the accuracy of you table.

Thanks for the replies, guys. I guess I left out a lot of info. What I am doing is designing a gantry style drill table for a guy that does electrical back-panels; mega small 10-32 - 1/4-20 holes and a few 1-1/4" PR hole saw bits. So all loading is in Z axis, powered by air slide. X and Y will probably be driven by large stepper and belt-slaved, dual ballscrew. Accuracy would be maybe .005 - .010, repeatability similar. Much of the backlash could be taken out with software if the machine is rigid enough, I hope. Could probably do with less accuracy, but I don't have much experience here.

What I think I need is something similar to a Thompson hardway, continuously supported, maybe 3/4 - to 1" diameter, and 7-8 ft long. Thompson is really expensive and not sure if they make anything that long. I tried to look up Black Diamond but their site was down. I am open to ideas.
I saw some stuff by VBX that looked pretty good but not fully supported rail. (http://www.vxb.com/page/bearings/CTG...rMotionSystems) I am interested in the Wisecarver V wheels but have no experience with them.
I hope this 'spains' a few things. Jeff

[ger21]

As was mentioned earlier, look at Bishop Wisecarver dual Vs at www.bwc.com or cheaper knockoffs at www.cadcamcadcam.com

[Al_The_Man]

It sounds like you have alot of the mechanics worked out, but for the application you have, I would consider taking a leaf out of the High speed punch machines book.
They use ballscrews, driven direct with low inertia motors so that 1000~2000 "/min is common.
They lay the sheet steel on a flat table and the material is gripped at one edge by pneumatic fingers, all you need for a guide is chrome steel rod with self lubricating sleeve bearings like Pacific Bearing Simplicity style.
There is no need to shuttle a table back and forth with this method, only the sheet.
This way the drill head only moves in Z not X & Y and you could increase the rigidity this way, as they do with a punch.
Al.

[jkpugh]

Originally Posted by Al_The_Man There is no need to shuttle a table back and forth with this method, only the sheet. This way the drill head only moves in Z not X & Y and you could increase the rigidity this way, as they do with a punch. Al.

Sounds like a clean way to do the job! I can not really picture how I would build this. Where can I get more info? Thanks.

[Al_The_Man]

This is the type of machine I was refering to, http://www.tramarindustries.com/equipment/11043.html of course you do not need the beef of a punch. but if you notice the table surface has ball rollers let into the surface for the material to roll on, the X&Y are direct driven by ball screw and the material lays on the table and is registered by pushing the plate into the open finger grippers, when closed they shuttle the material, relatively friction free, under the punch (drill) head.
As I mentioned before the XY can be guided by nothing more than relatively cheap chrome rod and self-lube bearings, if you go to the P.B. site and look up the Simplicity line, they have both Round rod and square tube type linear bearings.
Al.

[ViperTX]

The machine that Al has shown along with any other Strippit like machine is okay when you can allow the material to roll over ball rollers....it works because most of the material is subjected to a post punch/drill operation where the surface is abraded to remove any scratches....basically the post punch/drill operation adds uniform texturing or surface scratches.

If you can't or don't plan to have a post punch/drill operation....then a CNC router style setup is better.