New Machine Build- inverted table as base, 200X80cm

[technodream]

I want to make a large routing table for wood and plastics.

design inspired by MechMate and such- elevated "walls" fully support the X rails.
for the X axis I will use 2X 176cm INA linear bearings I found in the scrap shop.
Y carriage will be based on 80/20 and more INA linear bearings.

3 initial design questions-

1. I want to do the X axis movement as rack&pinion, using two 200cm spur gear racks (15X15mm profile) but am very worried about the accuracy (looseness,play) in these things. one specsheet says "Tolerance on single pitch +/- 20 μm, Tolerance on sum of pitches +/- 30 μm on 500 mm", is that good enough for my application?

2. I had an idea for a sturdy frame which will be easy to calibrate the X rails and assure they are parallel in all axes .
the frame will use a heavy steel table, such as the one pictured. the table will be inverted and the legs shortened to be about 30cm long. then I will bolt on an L-beam on both sides and use as a platform to attach racks and linear rails, as seen in the drawings.
supposedly after everything moves along nicely, I can weld the L-beam permanently and also weld some steel supports to the structure.

what do you think? what could be the advantages/problems? consider that the drawing is a draft and dimensions are approx.

3. for the Z-axis, I have found an old "micro-controle" 120mm linear stage, VERY sturdy, supposedly with 2um resolution. also found an old educational robot with a 350mm stroke linear stage (pictured, with my foot..), looks good, alum cart with plastic bush (see 500mm stage in pic) but the leadscrew itself has a springy 2-3mm "give" in the axial direction when a force equiv. of ~5kg is applied... all the way through the motor (can feel the shaft moving at the back of the motor where the knob is attached..)

which would you recommend for mdf, wood and plastic routing? I prefer larger stroke of course.. should I limit the axial movement or use it as dampener?

thanks for your advice!

[PaulRowntree]

There were no photos attached, but some thoughts ...
I think you will always need some adjustment mechanism to position your tracks, even if you weld after it is running smoothly. I used an old desk for my base and I have regretted it every day since : it was just too lightweight in construction. Make sure your table is solid and heavy enough.

You would have to check the specs on those Z stages. One sounds like an optical table device, which would not be fast enough for use with a cutting tool, and probably is not built for the forces involved. Most folks use a lead screw on Z. Anything with 2-3 mm of mushiness is a non-starter. The motor should not be used to stiffen the travel, since they are not built for it; use proper thrust bearings to constrain the shaft in the axial direction, and std bearings for radial forces. Or a combined approach with angular bearings (I have never used these).
Cheers!

[technodream]

oops. first time. uploaded again. you can see the table is pretty sturdy but I'm looking at other tables too.

and yes, it's an optical stage. but the diameter of the lead screw is about 9mm.

[PaulRowntree]

My optical stages are built for precision, not power and not speed. They get the precision from a closed-loop operation, which would be difficult to integrate into a Mach3 type control software. I think you would be disappointed. Plus, you probably want to avoid unsupported guide shafts on any axis; they will flex badly.

Check out CarveOne's build threads; he has gone the large steel table route with great results, and his build logs are quite detailed. Rack and pinion too! It is the thread called 'CarveOne's steel channel rebuild',


Cheers!