Laser cut mounting plates thickness
 

The laser cut parts came in the other day from Donald's Hobby. First I want to thank Donald for helping us all get our routers moving in the right direction! He had great communication throughout and got the parts done in a very timely manner.

When the parts arrived, the sharp metal ends had cut through the box and styrofoam peanuts were following the FedEx guy through the door. The parts were just laying in the Peanuts. In the future, it would be better to simply zip tie the parts to a sheet of heavy cardboard or 1/8" plywood to keep them from cutting their way out of the box and escaping into oblivion.

The bending job on the main car was kind of sloppy, as the bends were outside of the scribed guide lines. I'm sure our welder will fill the gap (he did not seem concerned) but the bender guys should be reminded that the scribed line should be in the center of the bend. I guess you could give them the end caps and let them see how they should fit as they bend them.

Thanks again Donald!

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The PK296A1A-SG7.2 motors say on the spec sheet that the MINIMUM thickness of the mounting plate should be 8mm.

Of course when the MechMate plans were being drawn up, nobody was planing on using those motors and the parts from Donald's Hobby came 6.3mm thick.

I'm not too worried about a 20% difference, but future batches of the motor mounting plates should be increased to 8mm as recommended by Oriental Motor.

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Here is a pic of everything you get in the box of laser cut parts.

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James, those motor plates say 6mm on my drawing - that is more than thick enough. I will look into why Oriental Motor want thicker.

The bending is not easy, and for a first attempt it doesn't look too bad. It appears as if the radius of the bend is a bit big. I didn't spec the radius on the drawing - I am just used to our bending guy giving an inner radius equal to about 1x plate thickness.

That 8mm might be because of the screw length supplied with the motors??. I have not found this spec - is it on the sheet that is packed with the motor?

Nothing to get too excited about.
The bending is typical of what I got.
I used the same laser cutter and a differnt bender than Donald did. Similar results. A few clamps and it will be fine.
Most important part of the Y-car is to be sure it is flat and square when you weld it
As for the screws that goes through the mounting plates, they do not bottom out and the plates don't flex.
The specs are just typical of guidelines.
Remember we run more voltage thru these steppers than the specs say to.

DocTanner

Finding the mounting specs took a little time, but I found them on the Oriental Motor site.

It appears that the 8mm minimum specification is for those who are going to use threaded mounting plates.

I cannot understand why they draw a distinction between through hole and tapped hole, being fussy for the one and not the other?? (I use through hole PK299 motors on these plates as well).

If I were Oriental Motor, my biggest concern would be for bottoming out the supplied screws because that can crack the gearbox casings. When a blind hole is tapped, the last bit of thread is not full diameter - "bottoming-out" can be more a case of the sides being forced out.

The only resistance I have to increasing the thickness of the plates (aside from not understanding the reason) is that the motor moves further away from the rack and the pinion gear has a risk of overhanging the tip of the shaft. This is not too serious either.

Here is the page that came packed with the motor, copyright 2005:

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After posting that Oriental Motor reference about the "threaded" mounting plate, I started to wonder just how I would be expected to use a "threaded" mounting plate with a gearbox that has "threaded" holes. It must be some secret method that's too advanced for us Americans to grasp.

However, it seems reasonable that with a non-geared motor, where a mounting bolt can't protrude through the face of the mounting plate, that using a 15mm long mounting bolt would protrude through the motor and 'almost' all the way through the mounting plate - less 1mm. That should work. The motor would be held securely in place. The plate would not only function as a mount, but as a heat sink, and regular bolts could be used to do the job.

Personally, I've milled motor mounts from 1/2-inch Delrin, 1/4-inch and 1/2-inch aluminum, and 1/2-inch polycarbonate. All the materials worked fine. Currently, my belt-driven gearbox uses 1/2-inch Delrin. It doesn't work as a heatsink, but it's plenty strong to be used as a motor mount.

The original mounting plates on my Shopbot Alpha were fairly heavy duty, but they were either 3/16-inch or 1/4-inch thick. So a 6mm thick mounting plate would be an excellent choice, as far as I'm concerned.

Interesting, but I feel the plate drawing showing 6mm does not need to be revised. Might add a note to the drawing saying that Oriental Motor wants a thicker plate for unknown reasons and to check that the screws are not binding at the bottom of the threads.

I don't think that the additional thickness requirement has anything to do with a concern about bottoming out the mounting screws in the gearhead, because other models of their geared steppers have thinner mounting plate specifications.

I would bet that it is related to the torque of the motor .

Looking at their drawings, the hole specified for the motor shaft is 35mm and our hole is 72mm. So we have even less material surrounding the motor mounting bolts.

I can call them on Monday and ask what the reasoning is, but it sure would not hurt to in the future use 8mm stock

James, they don't specify the type/strength of the material, only the thickness. They don't care whether it is plastic or titanium. I can assure you that it has nothing to do with torque, and that the 6mm steel plates would be able to handle at least ten times the torque of that setup. (My ShopBot hangs a motor off 2 screws only, from the side of 3/16" thick angle iron....)

The other motor models that allow thinner plates have different mounting holes and screws - lighter, shallower, shorter......

If we went to 8mm plate, some laser guys would do a bad job of the smaller holes and slots. I am going to keep that plate spec at 6mm.

Would be interesting to hear their objection to 6mm plate - please let us know.

No worries here, I'm not going to get new mounts made or anything like that!

They do state "Mount the gearmotor tightly against a METAL surface with good thermal conductivity such as steel or aluminum".

So if not torque, maybe heat dissipation....who knows?

Heat is a realistic consideration, but the surface area would then be more important than the thickness. Hmmmm, would they accept lead? http://www.mechmate.com/Forum/clipart/happy.gif

No worries here either James. It just came as a total surprise and it is mysterious. Some designer in Japan felt it was important enough to put on a doc. and it would be enlightening to find his reason. I once worked at a car factory producing Japanese cars and we had some fun with the Japanese drawings. The drawings were excellent, but the logic was "different", yet sound.

James, did you get any answer from Oriental Motor? Here are some pics of the 2005 SB mounting plates - the design has been changed since.

Today I did hear from Steve Simon at Oriental Motor. He said the motor mount should be 8mm and as large as possible, to both draw away heat and keep the motor from vibrating or mount flexing. I missed his call, so this was just on our voicemail. I'll call him back for a more in depth answer.

James,
I use the PK296A1A-SG7.2 motors, rest assured there is no heat to get rid of.

There is no flexing, the motor tensioning spring would stretch or steps would be missed long before any flexing could happen.

9 months as a proud Owner of a MechMate, No problems with any part of it.

DocTanner

Hi DocTanner

Good to hear from you again!

Doc, that is great news to hear. I'm glad everything runs cool; should last longer!

Hello Doc

Have you posted pictures of your MM? if so i can't find them.Thanks