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View Full Version : Another newbie thought



chunkstyle
05-20-2010, 02:00 PM
Hi all,

It occurred to me today that as I approach getting into adjusting my spindle to get it square to the table (using Gary's generous article on "tuning up the PRS gantry") there is really no built in adjustments in the machine. This seemed lacking as most of my other shop tools have been designed for being able to take out the eventual slop that will develope. As I look at the machine from factory there is NO adjustability to take out the eventual slop in the critical area of the spindle squaring to table. It would seem highly improbable that the machine will hold it's tolerance over time and the cabinet folks that responded to my earlier post titled "gut check" would seem to confirm this. Heck, my spindle isn't even square right out of the box!
Although I'm committed to the task of getting it squared as Gary outlines, would it not make sense for Shopbot to design some way to quickly and reliably set the spindle. I look at my bot and look over at my DeWalt GWI radial arm saw and wish some of it's adjustment features could be found on the bot.
One thought that occurred to me was that the two machines used eccentric bolted bearings. The dewalt has them in the roller head and the Bot has them in the bottom of the Z car.
It occurred to me that the eccentric bolt might be a good idea on the two front bearings of the Y car's end plates. This would allow the adjustment of the beams attitude to the table bed.
The second area would be to use an eccentric V bearings for one of the fixed stud V bearings at the top of the Z car. This, too, would allow the Z car to "pivot" up or down to the sole upper fixed bearing and, thus, change the attitude in the Y direction.
The thought would be that it would allow for quick and easy adjustment of the car to set your spindle square.
The folks at shopbot had concerns tha the x-car would be to heavy and the eccentric bearings would not hold their position over time. Maybe or maybe not. I hope they try it and see. What the heck else do you have to deal with this issue?
The idea of this post is that maybe there are any other ideas that would work similar to what I'm proposing as far as quick and easy routine adjustments that would hold their position adequately. Maybe someone's already tried this on theirs? Just thought that it might be a subject worth brainstorming on.
My two cents.

Gary Campbell
05-20-2010, 09:50 PM
Tim...
I am going to go with ShopBot on this one. Not for their reason, as I believe the eccentric mounts should be able to bear close to the same weight, but because I wouldnt want to chance them loosening or changing on me. I would like to see 3 V rollers (fixed)on the top tho.

curtiss
05-20-2010, 11:21 PM
One bot I saw a few years back had a a piece of angle iron welded to each side of the vertical z frame, which had 4 set screws that would micro-adjust the z axis attitude with a small wrench. Much like leveling a pool table.

Once the z was plum in both directions, tighten it up. Of course it may move a bit out of plumb when the bolts are tightened. Just takes a few attemps.

chunkstyle
05-21-2010, 08:47 AM
Curtis,

I think I saw that modification in a post with picture, too. It may have been on an older style Bot that I have even less experience with, but it had the same idea of a simple but accurate adjustment to get the z-axis square to the table.
Gary,
I dont know if the Eccentric shafted v-rollers would lose their positions or not but it would be nice if Shopbot could try it. I talked to tech support about the idea and they had not , as far as anyone knew at the time, tried it. I noticed that here is an eccentric for the concentric shafted v-rollers that BW makes. Perhaps a bushing, with the hex nut on the outside of the end plate would be less likely to "roll" out of position? Either way I havn't got the nerve to drill out my end plates to test the idea but I would hope that Shopbot would in their R&D dept. To me, the lack of any design to take up eventual slop has a feel of so much "non-serviceable parts inside" feel about it.
I have pulled my z-car off the gantry's aluminum extrusion three times last night, right after pulling the spindle off the Z-car. This was an attempt to shim out the upper V-bearing to get the attitude of the spindle, in the X-direction, correct. I'll have to pull it off again becouse I went a hair to far.
In speaking to Shopbot Tech support about the lack of needed slop in the z-car mounting holes for the spindle's mounting plate to be moved (in order to get the spindle plumbed up in the Y-axis plane) it was suggested that I drill the holes out just a smidge.
Clearly there has to be a better way as Shopbot is relying on their machines coming to us perfect (with the usual disclaimer of the possible rough handling in shipping). The lack of any adjustment would imply that Shopbots designers believe there is no reason to ever need to adjust the tool once set up and running right. I have a shop full of other tools from both old and new designers that believe otherwise.
Perhaps the Z-car is the answer since both the X and Y axis could both be squared from here. Something to think about. Gotta git back to work...

chunkstyle
05-21-2010, 08:49 AM
Whoops,
I meant to say there is an eccentric BUSHING for the concentric Shafted V-rollers. Sorry for confusion.

curtiss
05-21-2010, 11:59 PM
I meant to say plumb in both directions .... not plum. sorry for that confusion...