PR Upgrade.

[workingdog]

I have a stock rack and pinion PR with a ball screw Z. I am trying to scrape some funds together to purchase a new 4g controller .
#1. I would like to hear from anyone who has gone this route, as to what kind of results they achieved.
There is a lot of info on PRTs being upgraded but little on PR upgrades.
#2. It would also be nice if someone from Shopbot would get together with someone at Bishop Wisecarver and come up with a rail system that can be retrofitted or bolted to the PR's unistrut with a minimum of grief.
#3. I'm sure there are other PR owners out there that would be interested in buying a purpose built/engineered rail upgrade directly from Shopbot that we know has been tested true.

[Brady Watson]

Mike,
A 4G upgrade on a PR would be a very nice setup. I use Geckos (the drivers in the 4G) on many different machines running both small and large steppers. It will totally transform your PR with higher speed and better positional accuracy.

In terms of ShopBot engineering a PR rail system retrofit, I wouldn't hold your breath. There are a number of people who have added BWC rails to thier machines with good success. I would advise you to search this board as a few have posted examples of this upgrade and how they did it. It isn't hard, but it is some work...so be prepared to do your own engineering and get your hands dirty.

-B

[workingdog]

Thanks Brady,
I have searched the board and looked at the posted examples . I also have a post on custom CNC's board.There's a couple of very promising drawings posted under PR upgrade on that fourm.

SO!!! If anyone has any new photos of their rail upgrade, or better still, a CAD drawing that they would like to share, I would be very interested in seeing them before I start drilling into my unistrut.
Thanks
Mike Copeland,

[donchandler]

Mike.
What is the URL for the custom CNC board?
Thanks,
Don

[bill_lumley]

www.custom-cnc.com/ (http://www.custom-cnc.com/)

[donchapman]

I too have a standard rack-and-pinion-with-Z-ball-screw PR96 that has been a mostly very dependable but somewhat slow workhorse for 7 years and am also trying to decide what, if any, upgrades to make. The G4 upgrade and doing something along the lines of the BW rails both seem to make sense. Did you make a decision, Mike? Are there other PR owners out there who have made the G4 upgrade, and if so what have been your experiences? Have all the earlier reported problems with the G4 boards been solved?

[workingdog]

Hi Don,
I am still sitting on the fence on this. I do think that upgrading to a G4 without upgrading the rail and ball screw would be a bit of a waste.
I would like to find a rail system that is a little easier to install than the BWC. However I don't have a lot of spare cash to experiment with. That's why in my original post I was hoping Shopbot would get with BWC and come up with a simple solution or a cad drawing.The ball screw I can deal with , but I have not come up with a rail upgrade that I like yet.

[donchapman]

I tend to agree with your reasoning, Mike, although I still wonder whether the promised increase in smooth operation from the G4 board might be worth it even without a rail change. My old PR rolls pretty smoothly in all three axes when the power is off. If the G4 board really smooths the operation of the steppers I think I could at least double my speeds even if I didn't make changes to the rails. That's why I'm asking if there are any PR owners out there who have made just the G4 change and not yet upgraded their rails. If the G4 significantly helps even an old PR with utility strut rails, I'd make that change now and change the rails later.

[donchapman]

Everywhere I've said "G4" I've obviously meant "4g". Sorry.

[workingdog]

That is exactly what I plan on doing. Upgrade to the 4g. Then do the rails and ball screw upgrade later.
I am sure there are a lot of other with the same plan. So I am going to wait and see what comes up on this thread before I do anything with my rails.

[zeykr]

I have a PR that basically had a prt upgrade done to it - a prt Z axis and a prt control box. It still runs on the unistrut rails which are getting fairly worn. The new z axis and prt control box were a worthwhile upgrade and made it much more 3d capable. I think the 4g would be a good addition, but I'd also like to have an easy to install rail upgrade path at some point.

[donchapman]

Ken: How is your new PRT Z axis different from your old PR Z axis?

[zeykr]

The prt z axis is the blue rack and pinion type from an older prt. The PR of course had the ball screw system. The PR had been updated when I bought it by mounting a z from a PRT on it, and replacing the pr control box with a prt control box. Though I also now have a PRT with a spindle and vac holddown, the pr is still used and is a good machine.

[donchapman]

Thanks, Ken. The reason I asked is that in another thread Brady Watson recommended that Mike Copeland keep his ball screw Z rather than replacing it with a rack and pinion Z, but his recommendation wasn't in the context of upgrading to 4g.

Does anyone have any thoughts about the necessity or advisability of replacing the ball screw Z if I upgrade to the 4g board on my PR96. And even if the ball screw Z assembly itself is ok, should I replace the Oriental Motor PK268-02A Z stepper with a different one?

[Brady Watson]

After a flood of e-mials - just to clarify...I have not personally done PR conversions or upgrades.

I would encourage those interested in modifying their PRs to contact those who have already done the engineering and work to make it possible.

-B

[donchapman]

Brady: That's what we've been trying to do in this thread: To get owners who have upgraded their PR's to share what they've learned. Sorry if my last post inadvertently encouraged any of those private emails to you, since I'd much prefer questions be asked and answered on the forum for all to see and benefit from. I appreciate the quality of your frequent comments.

[richards]

The PK268-02A motor will work fine with a Gecko stepper driver. It is rated at 1.4 amps bipolar or 2 amps unipolor, so be sure to select the correct current limiting resistor.

Given the fact that the PK268 drives a ball screw, you already have a system that will multiply the rather meager torque of the PK268 to something usable. Although I have no idea what the tread pitch is on the PR, other ball screws that are commonly available have about 5 threads per inch. So a PK268 motor would have to receive 10,000 pulses to move the Z-axis one inch. (2000 ppr X 5)

If I had a Z-axis with a ball screw, I would certainly try using it with a 4g before even thinking about replacing it (assuming that it is in good mechanical working order).

[billp]

Don,
Years ago I took my old cable drive machine, and then sequentially upgraded it to a PR, and then a PRT. Based on my experiences I think the most important changes to be made on these machines would be ;
Switching the way the wheels ride on the unistrut (OR better yet, get rid of the unistrut altogether and go with angle iron/BWC "bolt on " rails). This eliminates the incredibly frustrating exercise of having to realign the 45 degree wheels to the original grooves in the unistrut.In the first three pix you can see how Jimmy A. , and Ed Coleman upgraded their rails.You can also see the last picture below which shows how Bob Dodd added the BWC rails to his machine...
Swapping out the ball screw Z axis for a rack and pinion version (reason for this is an increase in speed, not accuracy...). Plus it's the right time to switch from the smaller Z motors to a larger one
Changing the control system to a 4G board, for smoothness, and potential speed gains.
Here are a few pix from prior Forum postings which will show you some of the MAJOR improvements that can be made with a PR.

458
459
460
461

[donchapman]

Thanks Mike and Bill. You provided good info that will save me lots of trial and error. I'd like to hear more from other PR owners about their own upgrades. Looking forward to seeing you, Bill, in a couple of weeks at Wayne's Austin Camp ShopBot.

[edcoleman]

Folks:

A couple of the pics Bill posted above were originally reference in this thread:

http://www.talkshopbot.com/forum/messages/28/7776.html?1116029913#POST24321

The pictures are not "in" that thread, but there is a reference to this page:

http://www.colemanwoodworking.com/sb_rails.html

The rail upgrade I did to my PR was very easy to perform. I'm not sure it is the best mechanical design but it has served my purposes very well.

I have NOT done any upgrades to my control box (yet) - although I would sure like to....

-Ed

[tommyr]

Don,

I don't know if you have seen my recent cable driven PR upgrade. I have posted it on numerous forums.If not follow this link for pictures.

http://accurate-inspections.com/pr%20cnc%20upgrade/

The conversion was pretty simple, I simply stripped down my PR to the uni-struts, mounted some stock 1 1/2 inch angle iron to the existing frame. Bolted on some 20 degree racks and used over the existing wheels to ride on the unaltered
angle iron.

I used some flat 1/4 inch steel to make motor mounts for my new 640 oz motors.

That is the sum of it, took about four days to do the conversion and only needed a drill press and a hacksaw to do most of the work.

Pick up an linear actuator off of ebay for the z axis. All total spent somewhere around $1000.00 for all materials including the motors.

Tom

[donchapman]

Thanks Ed and Thomas for more great info and photos. Are your X & Y carriages held down just by gravity or do you also have a wheel or something underneath to limit upward thrust? If not, has that ever been a problem?
Thomas, have you noticed any wear on the relatively soft (as compared to the hardened BWC rails) stock angle iron from the wheels? I quess the grooves of the wheels are in contact with the angle iron so you don't have the problem I have with the sharp edges of the hardened wheels digging into and wearing the unistrut unevenly at those parts of the table where most repeated routing gets done, i.e. near the lower left corner. Thomas, I see where you left your carriage wheels mounted at the original 45 degree angle, whereas others have redrilled and mounted theirs to ride flat on top. Do you have any second thoughts about that or has it worked just fine for you?

[tommyr]

Don,

Do to time constraints and not having any prior experience in this area before this conversion, I took the simplest route possible.

Also not having access to a machine shop I used as much of the existing frame as possible.

Due to all the extra weight from the new z axis, angle iron and gear racks, the y axis has never jump off the tracks during cutting. So I have never gotten around to making a new hold down.
Although an errant plunge into the work area on the z axis will lift it off.

This has only happened while zeroing the z a few times and in my opinion is like a fail safe causing less stress to the machine and not damaging the bit.

The original wheels glide smoothly over the angle iron edge and after three months of use show no appreciable wear.

At first I had the wheels riding on top, but found that the original mounting allowed me to adjust rails better for square-nest. This is due to the fact that in a upright position the wheels have slop in the bearing that causes movement from side to side.

Tom

[donchapman]

Tom,
Your success with the cheap/simple fix once again remindeds me to pay attention to the concept expressed by the acronym KISS: Keep it simple, Stupid! Thanks.

[workingdog]

Hi,Don.
I would have thought that there would be a lot more botters interested in new rails to accompany the new 4g box.
What I think I am going to do is simple mechanically. Fasten some angle iron over the unistrut so the top wheels ride on the corner of the angle iron and the bottom ones still ride on the botton of the unistrut.If the wheels score a rut in the top corner of the angle iron, it could be replaced as a perishable runner. It looks like there is enough play in the set up to fit the angle iron in without having to change anything else in the set up.

[donchapman]

Mike, that sounds like a simple solution somewhat similar to Tom's, which seems to be working well for him. Please keep us posted on your progress. I'm probably going to buy and install the 4g box before I make any changes to my rails just so I can see how the 4g improves my PR even with the old unistrut. I've heard it gets rid of the moaning and groaning I often hear during moves and jogs. Then I'll probably follow your's and Tom's leads and make some sort of angle iron additions to my unistrut rails.