Tuesday, May 31, 2011

Print table installed

I had gone to considerable trouble to make sure that I sited the bolt holes in the MDF {medium density fibreboard} print table properly. To that end I designed a template for each of the brackets that would show me where the guide holes should be put.

Once I had the table suitably aligned, I was able to drill the guide holes with my Dremel tool quite easily.

I then removed the table and took it to the workshop to drill out the holes to #8 bolt diameter.  When I returned and tried to mount the board I discovered that the holes didn't line up.  I had neglected to mark the lower left corner of the print table and had no way of knowing which side our orientation matched my drilled holes.  We are talking about a few mm here, mind.   There were 16 possible orientations and that was complicated by the fact that the brackets were able to rotate around the z-axis linear shafts in  the xy plane.  After about the tenth possible orientation, I found one that fit 3 of the four brackets and just redrilled both the MDF and the bracket.  Mercifully, solid ABS is very amenable to drilling so other than having the lower right corner showing an extra set of bolt holes, it all worked out quite well. 

Hopefully, I will remember to mark the lower left corner the next time I build one of these.  The print table moves quite freely as the video will demonstrate.

Now all that remains is for me to reprint the z-axis cable grippers and mount them and the z-axis will be complete.


EdZ said...

Have you thought about adding counterweights to the cable returns? They're probably not necessary with a NEMA 23-driven thread rod lifting it, but if you wanted to use a smaller motor/faster drive in the future you could set things up so it need only lift the weight of the printed material.

Forrest Higgs said...

Counterweights would certainly go a long way towards reducing the force needed to move the print table. OTOH, balancing the system would also make it more prone to backlash error. As well, you will find that NEMA motors do not decrease linearly either in cost or power consumption as they get smaller. The one I am using, for example, draws about 0.25 amps and costs about $19.

chylld said...

looks like a good exercise machine you have there :)

counterweighting is a pretty clever idea... although like my design, forrest's actually benefits from being unbalanced as the weight of the bed works to our advantage

Bogdan Kecman said...

That is fairly light assembly, it could be moved even with nema23 direct drive, let alone trough studding. I'm not sure if the M8 has thread angle low enough to keep the bed in place but nema23 holding torque is more then enough to hold this bed in place.

Wrt Nema23 250mA are you sure tjat a coil current is only 250mA, that does not sound like a high torque motor, with nema23 ans 250mA I don't think you can get more then 2kg/cm of torque