How To Keep a ShopBot SQUARE

[roney]

The purpose for this new conversation is to get feedback from other botters on "squareness issues". What prompted me to start this topic is the fact that we just can not seem to be able to keep our SB square ie: y axis square to x axis. We have loosened the bolts on the carriage did the 3-4-5 deal, checked for loose pinion gears (not), I do recall that one fellow mentioned that he squared his SB by bumping it up against some bolts which he placed somewhere on his X axis rails. Is this something that should have to be done? Come-on how hokey. Ted at SB if you read this I hope that you will respond as well, because I had such high hopes for the use of my SB and those hopes are waning with each NEW problem that occurs. I mean that this tool should be able to be kept in squareness with out having to constantly check it or bump it against squaring bolts. Are you guys welding your carriages once they are square, if so do they stay square? Are you certain...I'm truly trying to get to the bottom of this situation. Weather I am able to get my SB square and keep it that way or not this has been my first foray into CNC routing and I am so glad to be here. But dog-gone-it these things aught to stay square and if they can't, then all the SB's capabilities are for naught.
Come on you guys, yea you with the fancy smancy auto leveling table and you sir with the laser leveler and you fine gentlemen from all over, I pose these questions to all of you, can the SB's really be squared by you and can they stay that way? Who among you I ask, claim to be able to square their SB into submission?
jrc

[danhamm]

Sorry Roney,I'm the guy who was "talking" about
the laser leveler, I don't have your problem,
my table I made is all welded construction .250
wall steel. about a week ago I ran a pencil
around to check level and square it was within
a thou. "so sorry"

[bill.young]

Roney,

My ShopBot is an early model utility strut tool that's been upgraded to R&P. I cut scarf joints for boat planking with my ShopBot, so I'm pretty fussy about it staying square. I spent a lot of time when I set it up getting the rails straight and everything square, then tightened all the bolts as tight as I could get them. I used to check for square every morning when I started my ShopBot, but now I just do it occasionally and it's always where it should be.

After seeing the PRT tools it's hard to imagine that you couldn't get the bolts tight enough to keep it square under normal conditions, so it sounds like it's somehow being driven out of square by the motors. Does it only get out of square when you're cutting, or does it do it when it's just moving back and forth?

Bill

[edcoleman]

Roney:

I had some "squareness" issues a while back. Once it was the fact that the bolts were not quite tight enough, the other time occurred when I racked the machine by mis-typing a command and missing a decimal point. Since I've torqued everything down tight and added limit switches to ensure that "I" don't hurt the machine, everything's been square.

-Ed

[fuzzygrub@sinclair.net]

I had the same problem untill I adjusted the (bumpstops, limiters, whatever they are called on the bottom of the Y-axis). The main problem was actually driving my machine beyond the table limits and racking it out of square because the torque of the motors was enough to twist the connection at the Y-axis carriage bolts loose even though they were tightened pretty good. Since adjusting the (bumpstops) to square on both ends the problem has not reaccured. Anyway, It might not be the right solution, but it worked for me. I suppose if I exchanged the 305 oz steppers for a few 100 oz models this problem wouldn't have accured..N-O-W-A-Y!! By the way: watch out if you do decide to weld the carriage, metal tends to warp towards the weld side.

[roney]

Dan,
In your response to my question I sensed that I may have offended you and possibly. In no way did I intend to, in fact I'm extremely impressed by what you, Mr Seim and others are able to do with your SB's. However, we feel that we have properly assembled our SB and overly if not properly torqued our bolts...Dan, my problem is not with our table frame but with our moving carriage...
To the other responses thanks and guys keep 'em coming...BTW if any of you guys find yourselves near Gettysburg, PA contact me, if by then I'm still not square maybe you can square me up (in exchange I'll show you what I can of The Underground Pentagon and Camp David...plus we have an popular and awesome hang-gliding site as well...
jrc

[bill.young]

Roney,

What are the symptoms when it gets out of square; does it go out of square as soon as it starts to move, or does it start out OK and then gradually get out of square? Does your tool move smoothly, or does it seem like it's missing steps? What kind of computer are you using?


When it gets out of square, is it always out of square in the same direction? In other words, if you square your tool up and then tell it to move some distance, does one end of the carriage always move the correct distance and the other end always move the wrong distance? After it's been moving for a while, are both x-motors about the same temperature?

Bill

[danhamm]

Roney,

No you did not offend me, But I have been thinking about your problem, I had a driver
transitor burn up "my own fault" the bot still
ran but the cuts wouldn't match up, I think
thats what Bill up above is getting at too.
Maybe one motor is not working properly and acting as a brake,driver board wiring, connections,if you sqaure it up does it go out
immediatly or does it take awhile,

[Gerald D]

Roney, maybe you were thinking of me when you said: "I do recall that one fellow mentioned that he squared his SB by bumping it up against some bolts which he placed somewhere on his X axis rails". These are the photos of the arrangement: (the mods are in red oxide primer color)


563.jpg

564.jpg

565.jpg

You can see a short length of angle iron welded to each of the two y-carriages and four adjustable stoppers (long grub-screw and lock nut)welded to each point of the x-rails.

Regarding the locking of the y-gantry to prevent "racking" - we have got small tack welds of the rails onto the carriages, but this is not meant to stop the racking. The welds are mainly to keep an exact parallel distance between the 2 rails. This is absolutely critical for the v-rollers sitting on top of the "sharpened" rails.

While we were fiddling with the squareness setup, we found that the rails did not keep their distance apart, causing the y-carriage rollers to start lifting off the rails. This lift was never repeatable and so the squareness was a secondary issue until we could be sure that the v-rollers were properly seated at all times. My guess is that a lot of the squareness issues are really caused by rails that out of parallel.

May I add that we now only occasionally bump against the stops on purpose. If we have reason to doubt the squareness (after doing something silly) then it is a very quick and reassuring check to go and find the stops. Also, if we hit the stops by mistake, then we know that we have not stressed the squareness of the gantry, and we can immediately carry on working with the confidence that nothing was damaged.


566.jpg

[sheldon@dingwallguitars.com]

Gerald, I really like the way you've mounted the X rails.

Roney, is it possible that a gear might slip by a tooth or two under heavy load? I had that happen last night, so will be setting the springs a little tighter.