Deflection in Z carriage

[bleeth]

Yep-Gerald, I recall a similar discussion about y alignment and stiffness in which you discussed your solution of a spot weld on one of the bolts to maintain rail distance accuracy. I'm wondering if the angle bracket solution wouldn't kill four birds with the same stone; distance accuracy, anti-wrack effect, constant squareness, and chatter. Since we are dealing with a big "erector set" some basic bridge/span type gussetting should improve the overall charecteristics. Eliminating chatter and hence vibration should also result in bolts throughout staying tighter and reduce maintainence cycles.
One would need to make sure the y rails are properly squared and then make sure the folded profile (strut) is also aligned. I have thrown a dead straightedge on the side of the strut and seen that it is NOT perfectly straight and so some slight shimming of the angle bracket may be necessary.

[gerald_d]

Dave, are you trying to stiffen your...

- y-car (the small one that rolls on the gantry in the y-direction) and that is often blamed for cut quality?

or:

- the gantry (the big animal that rolls across the table in the x-direction) and that is often blamed for out_of_squareness? (and what I tacked together)

Carl is talking of ways to hold the little y-car square to the gantry. Other guys have used a second y-motor for this, but they say they don't need a second y-motor when they stiffen up the little car. Welding stiffener gussets to this car is a very simple thing to do (if you can weld) and you can easily make a stiffer car than the Alpha.

For the big gantry, some brackets can be added to make it as stiff as the Alpha, but this will only help with squareness and not really with cut quality.

[stevem]

It cost me approximately $180.00 to fabricate a welded steel X gantry. It shouldn’t cost more than $75.00 to fabricate a Y carriage, including paying a professional welder. I am currently experimenting with cutting wood (normally I cut plastic at 150 IPM) at 350 IPM on a PRT machine. Results are good so far with no chatter marks.
8910.jpg

[gerald_d]

Steve, I still think that is the best gantry design I've seen on a SB!


What material/size are the two main beams?

And, if it is not asking too much, could you mail me a better photo please? gdpost(at)gmail.com

[stevem]

Gerald, You're making me blush. The tubing is 3 X 2 X .1875" on the drive side and 3 X 3 X .1875" on the other side.

[bleeth]

Gerald: My last post on this thread addresses the gantry. SB's system has been to bolt a set of holddown brackets under the strut to the rail and from what I understand the alpha uses a slightly different shaped version of the same bracket cutting down on the amount of spacing necessary. I think angle brackets or gussetts laterally fixed would do a better job. To stiffen the car and hold it square on the "classic" I see a similar system mounted at the four inside corners from the car struts to the carriage. It seems to me step one is to make sure the gantry rails stays parallel and don't wrack. It's shifting while pushing through plywood all day will result in the holdowns getting pushed out of place and then here comes the bouncing car and chatter!! (As well as parts that are supposed to be the same size being different). I have found that the gantry being kept square is a more often occuring malady. In heavy use though, any retweaking of the alignment that needs to happen on a regular basis when no extraordinary shocks to the system have occured is more than there should be.

[bleeth]

Steve-6ips with a PRT? FANTASTIC. If you pull that off driving a bit through full width 3/4 ply with complicated shapes you have made a believer of me. Please send me some more pics or a sketch

[Brady Watson]

Dave,
Stevie is leaving out a few details...such as his Mach2 control software conversion. Using this setup with twice the voltage on the power supply, you can effectively double or triple your move speed. The higher voltage pushes the torque band higher in the RPM range. You will however, need new stepper drivers such as Geckos to make use of Mach2, since the Allegro drivers in the SB box are both soldered in and limited to about 44v or so.

-Brady

[bleeth]

Brady: You beat me to it-I had a chat with Steve today and he filled me in on all of modifications. As he put it: "There isn't much shopbot left and soon there will be less." He has done a lot of what I was thinking about vis a vis the frame components but before I go quite that far (It's not the cost of the steel and welding, it's the overall time involved) I want to try some of the simpler things to stiffen it all up.