Budget PM-20MV conversion

[kkaylor]

Hello all! Long time reader first time poster. So, my goal is to pinch the penny's on this build. Originally was going to do a budget X2 build, but this PM20 fell into my lap and decided to convert it instead.

Ordered the lest expensive quality drivers, powers supply, and stepper motors I could find:
3) KL6050 drivers
3) 570 oz steppers
1) 48V/7.3A PS
1) C10 BOB

Total cost so for $386.63

I just graduated college with an economics degree, so i need to keep this "economical". (pun intended) I also have more time than money right now.

[kkaylor]

I have a few questions to other PM25/20 owners.

1) The x axis acme screw on the left side is missing a thrust bearing. (see pic) is that normal? It has an outer one, and the right side has and external and internal thrust bearing.

Also, any tricks to removing the thrust bearing cover? Its wedged on pretty tight.

2) There isn't a stub inside the spindle for the R8 collet key-way to lock into. It works okay, but my X2 has that stub.

[SCzEngrgGroup]

You NEVER put thrust bearings at both ends of a screw. One end takes thrust the other must be free to float, to accommodate thermal expansion.

Regards,
Ray L.

[SuperFlyLoser]

I have a few questions to other PM25/20 owners.

1) The x axis acme screw on the left side is missing a thrust bearing. (see pic) is that normal? It has an outer one, and the right side has and external and internal thrust bearing.

Also, any tricks to removing the thrust bearing cover? Its wedged on pretty tight.

2) There isn't a stub inside the spindle for the R8 collet key-way to lock into. It works okay, but my X2 has that stub.

1.) Ray is correct on that. One end is supported with just a bearing and the shaft is allowed to slide during expansion/torque. And the other end is the one that has the thrust. On mine the thrust end is the one that I mounted the stepper to.

2.) There is supposed to be a screw that goes in the spindle that keeps the collets from spinning. If you take your spindle out you'll see a hole on the outer part. Turn the inner part and watch for the hole where the screw goes in. It might be missing.

SFL

[SCzEngrgGroup]

"There is supposed to be a screw that goes in the spindle that keeps the collets from spinning." - And that screw is COMPLETELY unnecessary! If it's out, I would leave it that way.

Regards,
Ray L.

[hoss2006]

I can vouch for your electronics choices kkaylor, they work VERY well together and you'll be VERY happy with the performance.
Do you plan to run STOCK screws or go to ballscrews?
HOSS

[kkaylor]

Thanks for the quick responses everyone!

Hoss! Glad to see your posting on my thread. In my eyes you are the Elvis Presley of the bench-top mill world. Actually getting a little Hossmania as I write this.

I was worried about taking on CNC conversion by myself, but with the help of all you guys I'm sure I can get through it.

I plan on using the stock lead screws. After cleaning, lubing and adjusting the Y axis split nut, I have no noticeable backlash.

The electronics are due to arrive tomorrow, I'll post some pics shortly of them and how I plan to wire them.

[hoss2006]

Why thank you, thank you very much.
Looking forward to watching your build.
Hoss

[asuratman]

I just graduated college with an economics degree, so i need to keep this "economical". (pun intended) I also have more time than money right now.

Economist become machinist, a lot of chance in machine world.

[arizonavideo]

Good choice not getting the X2 and starting with a PM-20. Much better machine in the long run.

The stock lead nuts are much better on the 20 compared to the RF-45 mills so it should work OK for the X and Y. With CNC you will want to float a bearing or at least add a plastic bushing on the end of the X screw to stop it from rattling around.

You will have to have some backlash with the stock nuts. At zero backlash any lead screw error will cause a tight spot or the nut will wear until it is not tight anymore.

You will have to keep them oiled and adjusted and expect some wear as they break in.

The Z is a bit more of a problem because of the friction of the stock screw. You might want to go to a ball screw from the start on that but I have not looked at hoss's plans to see what he did. If you have to run belts it might be around the same cost to go to a direct drive ball screw.

Have Fun.

[kkaylor]

Hello All!

Got my steppers and drivers last week and in the process of stuffing them into an old PC and wiring them up with 18 awg.

Been working on my X and Y stepper mount design, on paper, I don't know CAD yet so I'll have to explain it. My general idea is to use 3/8 by 2.5" aluminum plate to make legs to mount to the table. I also planned on using the same aluminum to make wide mounts that attach to the left table endplates so that I can use the same screws that hold it to the table.

Found a good deal on lovejoy couplers CNC Stepper Motor Lovejoy Coupling 3/8" X 5/16"& spider | eBay from ebay guy carolbrent. Does anyone know if these can be tapped? Also, the he sells "spider tightners". Does anyone know what these are and if there helpful?

Thanks!

[hoss2006]

You won't be happy for long with lovejoys especially ones that need "tighteners" to "take out the slack in the lovejoy coupling set to make tighter for CNC applications." this means backlash is a problem.
Get some zero backlash Oldham couplers.
I use these from Mcmaster.com on my 0704.
Part# 59985K113 1 inch Hub, 5-16" bore,
Part# 59985K18 1 inch Hub, 3/8" bore (or bore to match your motor shaft)
Part# 59985K63 Acetal Coupling Disc
Hoss