Upgrading the PRT-Continued from 2007 Archive!!!

[ken_rychlik]

I like the wonderfull custom e-stop mounting system you have!

Kenneth

[bleeth]

Yeah-The penalty of having it located in such an accessible location has been having it creamed umpteen times by rolling stock carts. I'm amazed it still works! Funny thing is-in all the years we have never used it once. All users race to the space bar if they want to stop it quick.

I have my first construction challenge. Somehow a math miscalculation led my x rail spread 1 inch narrower than the distance between wheels. I have a choice of putting a pillow block (1/2" x 2" x 10') under the extrusion and offsetting the mounting of it, using spacer washers between the gantry plates and the wheels, or having the y extrusion milled down 1 ". They all have their plusses and minuses. The quickest solution is obviously longer bolts and washers but the concern is how much stress the bolts would be carrying. They are 5/16" and 1/2" worth of unsupported length seems a lot. The other two means due to no weekend supply the project is postponed and we have no cnc next week. That would be a problem businesswise.
Anyone with enough knowledge of the bolt strength think this would work?

[gc3]

Grade 8 bolts come to mind...and maybe fender washers if possible. The extended bolt will get you running for Monday...maybe you can schedule a better "redo" at some point soon.

Gene

[ken_rychlik]

Given your choices, I think I would shorten the Y pieces.

Can you show us a picture?

Kenneth

[bleeth]

The extended bolts will put the motor pinions out. I can deal with that on a temp basis but not long term. I'll put them in for now and add the width via the wider block under the extrusion for a permanent solution. We'll see what challenges tomorrow brings!!!

[gc3]

Photos pls if possible, thx for the updates...

Gene

[bleeth]

OK: Got the extended bolts and verified it will work but will also require moving the pinions out on the motor shafts. This will be temporary as I will pick up a new top pillow block that is 2 1/2" wide and replace next weekend. This will be fairly easy instead of modifying the gantry to be narrower (don't want to lose an inch of y travel) or adding a block underneath (too much teardown to get there. My original numbers were correct but my metal supplier had 2" on hand and when he volunteered it for almost no cost I figured it would be wide enough for the extrusion and the rack but forgot why I had originally called for 2 1/2". The penalties of a project going on too long or maybe the failing memory of a "Senior" member!!

Here's a closeup of the current pillow block, a wheel with the spacer washers, and a wheel without. You can see that the larger diameter wheels (number 3's instead of the SB 2's) from Superior bearing required a bit of trimming to the gusset-easy to do since it was not fully assembled when I figured that one out.

[ken_rychlik]

How did you come by the prs gantry?

You can use 3/8 grade 8 bolts without the cam adjusters.

Kenneth

[gc3]

Does the 8020 run the length of the c channel? Did you attach the 8020 only where the old rail holes were? What will be the new hold down for the Y car?

Gene

[bleeth]

1. Bought end plates, gussets, motor plates, and z from SB. Extrusions and extrusion nuts from Bosch-Rexroth, hardened rails and wheels from Superior.
2. Getting metric around here is pretty easy. During the week there is a nut and bolt distributor, limited but regular stock at Ace Hardware, and highly limited at the orange store. I have bushings for the wheels and the right size is 8mm like most of the extrusion bolts.
3. Yes-10 foot of 45/45 for each side and 400/800 for the beam. The beam was an adventure since the first one came damaged and the second one too long! The Bosch distributor did all they could though in the way of customer service and picked up the tab for a local machine shop to cut it to the right length and mill it square.
4. I added new holes in the steel beam centered between the old ones and drilled them just a little oversized for some adujustment. The control side has always been the Y-0 as one of my original beams was not "sterling". The high side I took quite a bit of time test fitting and lining the new holes up with a laser. If you ever need one and can afford it Pacific is the way to go.
5. Since the rail is on the 3/4" pillow block I plan on hard bolting the motors. That will give me the same hold down as SB.
I'll find out tomorrow (hopefully) if that works. There isn't much original engineering here. The only real change from SB standard system is the x wheels. I just wanted to do it myself from assembled parts for the exercise. It probably would have cost me not too many more dollars but a lot less work to just buy a full conversion gantry from SB. Ted and Frank have probably been chuckling over it for a while now since I first started talking about doing it this way with Ted at Gary's camp a couple of years ago.

Speaking of the orange store I need a few bolts and some hacksaw blades and left my wallet home. I'll skip ahead of the order I was going to do things and do some gantry work out of sequence here cause a 1 hour round trip is too much of a *&&%#$* pain.