Hardened Rails on PRT Alpha X and Y

[harryball]

I finally installed the hardened V rails on both the X rails as well as the upper AND lower Y rails on my PRT Alpha.

My rails were very worn, they have been ground to shape more than 6 times now (I lost count) and I was not looking forward to doing that again. It's not hard, just time consuming. This time I went ahead and ground them aggressively using string and a straight edge to get them flat on top. I also ground the sides to remove burrs and make them smooth on the side where the hardened rail would be installed. I didn't grind all of the V away, just enough to make sure it was FLAT and the rail cap would rest on the top edge.

For the X rails and upper Y rails it was pretty straight forward. I used T2 V rails from SuperiorBearing.com with 13/64" holes every 3". First I ground the rails, checked them, put the rail cap on and placed a spring clamp between EVERY set of holes all the way down and added a spring clamp on each end. I then used a 13/64" bit to drill the holes. I used M5 x .80 x 14mm button cap screws with nylon lock nuts and a washer on the mild steel side. That went well with the most tedious part being drilling. I repeated that process for the upper Y rails. I purchased a dozen 13/64" drill bits, I ended up using 6 of them for both X and upper Y rails.

For the lower Y rails the process was different. I clamped the rail caps in place with a combination of Bessey and regular clamps to make sure it was in position and would not move. I then used a self centering bit (like you'd use do drill hinges) and made a divit in every hole to help center the bit for the next step. I then drilled in the center of each hole with a 4.2mm bit all the way through. After that, I used a 5mm tap and tapped each hole. Then installed the same M5 x .80 x 14mm cap screw along with an M5 lock washer. That went reasonably well but be sure to buy at least 2 taps, there were 46 holes total and my first tap lasted for 44 of those.

All of the above was done AFTER making doubly/tripplely/quadrouplely SURE the rails were flat, smooth, spaced correctly and parallel. To give you an idea, I spent as much time measuring positioning and double checking as I did drilling/tapping/bolting the rails in place. When you do the lower Y rails this way the entire rail is now PERMANENTLY in place as you have effectively screwed the entire rail to the gantry cross member 23 more times in addition to the bolts with T nuts.

If you have questions, let me know.

Photos:
1676 shows the X rail with the spring clamps and the end spring clamp
1677 shows the long X rail shot with spring clamps
1679 shows the transmission jack we used to handle gantry
1683 shows the clamps on the lower Y rail with some of the bolts already installed and the tap I was using.

/RB

[Brady Watson]

Looks great! Wait til you do some cutting!

For others that don't know...SB sells a complete upgrade kit that includes the hardened rails already mounted on the angle portions. You remove your old stuff and chuck it in the recycle bin. No drilling or complicated assembly to be done on your part. It's a few more bucks than doing it yourself, but time is money.

-B

[bobmoore]

Do you have any more pics of your Y car. I have a PRT with the original set up and I like the look of what you did with it. By the way, what was your approximate cost of the rail upgrade.
Bob

[Brady Watson]

By the way, what was your approximate cost of the rail upgrade.

I have no idea what current pricing is. Give Dianne a call: 1.888.680.4466

-B

[harryball]

Looks great! Wait til you do some cutting!

For others that don't know...SB sells a complete upgrade kit that includes the hardened rails already mounted on the angle portions. You remove your old stuff and chuck it in the recycle bin. No drilling or complicated assembly to be done on your part. It's a few more bucks than doing it yourself, but time is money.

-B

That's good to know, I did not know they offered that option... but then I'd already purchased most of my stuff and love an adventure. :eek:

[harryball]

Do you have any more pics of your Y car. I have a PRT with the original set up and I like the look of what you did with it. By the way, what was your approximate cost of the rail upgrade.
Bob

Bob,

The Y rails were about $60 each plus S&H. They are about 68" long and there are 4 of them. I had my X rails already, they are 120" if memory serves and I don't recall what I paid for them but if the math holds they should be less than $120 each. Shipping is a little pricey due to the length.

I ordered the bolts/washer/drill bits/tap etc... pretty much everything from Amazon.com. I have at most about $100 in misc parts and tools I didn't have on hand like a broken tap extractor.

As for time (NOT including grinding and overly paranoid measuring) it took me about 3-4 hours to do the X rails. I spent about 1.5-2 hours on the upper Y rails. I was not in a rush and took my time. It wasn't hard but it did wear on my shoulders. I used a dewalt 18V drill, if I'd had a corded drill it probably would have gone faster. For the lower Y rails, off and on I spent a total of about 4 hours drilling/tapping and bolting them down. Grinding etc... will depend on the current condition of your rails.

The V rail caps were placed one inside and one outside, this keeps the V rollers in line since the caps don't center the new V directly over the old V. The lower Y rail V rollers did need an extra washer to shim them down but were otherwise very close to the same.

/RB

[lalogiagorral]

how do you ground to shape on the rails

[barrowj]

Santiago,

Based on his writeup, he ground the angled part of the rail until it was just flat, probably 1/4" of the angle. He stated he used and drill and probably a grinding wheel. I would use an angle grinder but if someone does decide to do this be sure that you do your best to be absolutely level and I would use a 9' piece of flat steel to be sure it was the same height all the way from both ends.

I may do it his way, a lot cheaper I believe than buying the premade rails from ShopBot. I did get pricing and if I recall it was over $2k or somewhere in that range.

Joe

[harryball]

how do you ground to shape on the rails

I'd used an angle grinder in the past, I found it removed too much metal too fast for my comfort. I use a 3/4" diameter round grinding point in a rotozip tool. I would mark where I needed to grind, work it down, check, repeat etc... I also used an open bastard file to do the final dress on the rails.

I used a small combination square as a depth gauge. After my first grind to get the top right I found the lowest point on the rail and set the gauge to that depth then brought the rest of the rail down to that level. I could see with some back light (a small flashlight) if the end of the ruler against the bottom of the rail was tilted away (more grinding) or flat (correct level) or tilted toward (ground too much). I will probably have to post a picture of that for it to make sense.

It's kind of a art but not difficult. I've done it maybe a dozen times so I'm pretty good at it now. Get an old piece of angle iron and practice first. In this case I just took it further than if I was going to use it as the final rail. I made sure the top of the grind was wide enough to catch all the rail cap.

/RB

[harryball]

Santiago,

Based on his writeup, he ground the angled part of the rail until it was just flat, probably 1/4" of the angle. He stated he used and drill and probably a grinding wheel. I would use an angle grinder but if someone does decide to do this be sure that you do your best to be absolutely level and I would use a 9' piece of flat steel to be sure it was the same height all the way from both ends.

I may do it his way, a lot cheaper I believe than buying the premade rails from ShopBot. I did get pricing and if I recall it was over $2k or somewhere in that range.

Joe

An angle grinder is faster but be very careful, you can dig a notch out in a hurry. In the case of the rail cap that's not a deal killer as long as the high points are all level and not too far apart the cap will compensate for a few over ground spots.

I was not aware shopbot offered a pre-made hardened rail set (I started this project over 2 years ago) so I never priced it. For DIY figure about $600 total for parts using your existing angle iron rails and allowing for a few tools, new grinding stones etc...

If you are familiar with grinding the rails, your bot is already in adjustment and you had all the parts laying around then two people could do this job in a good 8 hours day. My Son helped me with some of the lifting but I did the job mostly by myself so it took me a while longer.

/RB

[bleeth]

If someone would like to go for re-grinding their rails with an angle grinder then they are best off making a jig for the grinder so that it runs consistantly. There is a "do-it yourself" build a cnc forum that tells how to do this. I have not done this but have heard that it works well. www.mechmate.com (http://www.mechmate.com)

When buying the "complete upgrade kit" from SB you get a lot more than just the hardened rails. There is a lot of precision drilling/countersinking, and tapping required on the pillow block to do it right. I upgraded my prt rails, y rails first (which was pretty easy to adapt right onto the existing angled rail but touchy to adjust perfect), and then x rails when I upgraded the gantry as well. I did it as diy project by starting with an extrusion and then a 1/2 thick pillow block with the hardened rails mounted to it. It was quite a bit of work, although for me it was a pleasant "tinker" project break from the normal cabinet work.

[Kromet International]

How many hours do you estimate that you ran before you had to change the rails? I'm curious since we have two shopbots and two more on the way, I would like to know if we should be keeping this kits in house?

[bleeth]

The changing and/or re-grinding refers to the mild steel rails used on older PRT's. I haven't heard of anyone needing to replace the hardened rails used on PRS models due to ordinary wear.

[Brady Watson]

Jeff,
ALL PRS machines came with hardened rails standard. A lucky few somewhere in the middle of production got hardened stainless rails ;)

This isn't something you'll need to worry about.

-B

[harryball]

OK, here are a couple more pictures of the gantry per request. It's been running great, much smoother and the cuts are cleaner. After 20 or 30 more sheets I'm going to go through and check everything, re-torque etc...

[David Iannone]

I just got the Kent CNC dust foot recently and miss the router bit being in front (been using the SB dust foot for years). I am gonna flip my Z 180 degrees when I take it apart for the rail upgrade. I learn more from looking at pictures.

Thanks,
Dave