Flange mount for alpha motor shaft

[3imoh]

Howdy-

I would like to build an indexer (of sorts). I am trying to find a source of a flanged shaft mounting plate that would allow me to mount various plywood bases to an alpha motor. I am picturing a keyed plate 2-4" in diameter that has a few mounting holes around it.

I have not had any luck with my usual sources (mcmaster, msc, grainger), though I may not be using the proper term for this...

thanks for any suggestions,
-howie

[Gary Campbell]

Howie..
Try Penn State Industies www.pennstateind.com (http://www.pennstateind.com) they have many lathe associated parts... you may need an adapter, but I am sure you can find what you are looking for there.
Gary

[3imoh]

Thanks Gary-

Those lathe faceplates are close to what I need...hopefully I can find one that would just slide on the motor shaft instead of needing to be threaded.

-Howie

[Brady Watson]

Howie,
I doubt it - an Alpha output shaft is 12mm. Shopbot uses a specially machined adapter to go from the motor shaft to the chuck that comes with the indexer. You REALLY need to have a good positive lock between the motor and the faceplate/chuck - or you'll risk permanently damaging the shaft of the motor.

Also keep in mind that a 1:1 motor will be significantly sloppy at diameters greater than 3" or so. The 10:1 motors that come on the Alpha indexers step at a much finer increment than a 1:1. So...not to sound discouraging, but these are just some things to think about.

-B

[3imoh]

Good points-

The motor is actually a 7.2:1 geared PRS motor...It is an extra that is the result of switching from a tandem to a dual z (long story). Anyway now I am wondering if this is going to have enough resolution at the diameters I need...The max diameter I will be working with will be 44" or so. I would not need to spin this very fast, but would like to have it position as accurately as possible. Wonder if the 7.2 would work or if I need to send this motor back to SB and try to exchange it for a 10:1...it has never been used.

-Howie

[Brady Watson]

Yikes! 44" is massive...and you're going to have some unique challenges. 1st, the best possible step resolution with a 7.2:1 motor that you could expect (with 2482.xxxx UV) would be 0.056" per step @ 44". That's pretty coarse. 2nd, and most obvious is, you'll need a mighty long Z axis to be able to deal with a range of diameters from 0 to 44" - or at the very least, a reliable way to raise and lower the entire indexer, which I can assure you is not as easy as it sounds. Do-able, but not easy if you want to keep things lined up, which is the entire battle with indexing.

It all depends on what you really need...if the 7.2 isn't fine enough for you, you may want to look into a 50:1. It'll have gobs of torque (which I can gaurantee you won't have enough of with a 7.2:1 out at that dia) and you won't need to turn it that fast - plus you'll get a much finer step resolution, which is what you want when indexing large parts. You can keep your 7.2 motor and build a belt reduction for it. I currently have a 10:1 stepped down with a 3:1 belt reduction to give me 30:1 overall. This gets me in the 12-14" diameter range.

-B

[3imoh]

Ok,

If I figured this out right, with the 7.2 motor I would be looking at 10 steps per degree. At 44" diameter that would be .39 inches per degree or .039 per step. I think I could live with that. The disks I will be spinning will weigh around 15 lbs, and the shaft of the motor will be more or less horizontal. Does anyone have a feel for if I need to look into a lower geared motor? Guess I should figure that out before I worry about the shaft mounting.

-Howie

[3imoh]

hi Brady-

Looks like we were posting at the same time (more or less).

I am planning on mounting this whole affair on the end of the table. so I would pretty much have the floor to the top of my z...I have a 14"z on the prs, so I should be ok there. the disks I will be spinning will only be 2" thick, so this will not really be a standard indexer mounted at both ends.

I am only going to be cutting 2" or so into the outer edge of the disk, so I don't need to go anywhere near the center...

I think I will look into the 50:1 motor...wonder how much that will set me back...

thanks,
Howie

[richards]

Howie,
The PK296A2A-SG36 costs $268 directly from Oriental Motors. As far as I can tell, 36:1 is the highest ratio offered online for the PK296A2A motor. Take a long look at it's torque curve (maybe I should say torque drop). At about 30RPM it takes a nose dive. Below 30 RPM it has impressive torque.

[Brady Watson]

Howie,
Is this an Alpha motor or standard motor?

-B

[3imoh]

Thanks Mike-

Is it possible to run that motor using an alpha driver? I have an extra driver in the control box. I know it does not have the position feedback. I guess the other option is to do a gecko setup similar to what Pat and Dirk have done.

The Oriental Motors site does not list the alphastep motors seperate from the controllers. Surely there is a way to order just a motor (though I can guess they will be spendy).

Brady, if you don't mind could you describe how you calculate the steps per degree on an indexer setup? I was going off of this in the manual, and came up with a different value that you did for 44 inch work...just wondering if I have this right.

--
Computing the Unit Value for an indexer would be done as follows, assuming you want to express the rotary motion in degrees. With an indexer having a 10:1 gearbox and with the alpha driver set at 500 steps/rev, we would have: (10 * 500) / 360 = 13.8889 [or, 13.8889 steps per degree].
--

So with a 7.2 motor that would be 10 steps per degree...with a 44" disk that would be .038 per step (.383/10). With the 36:1 I would be looking at 0.00766 per step, hopefully.

Another question...could I switch to 1000 steps/rev on the alpha driver at get away with the 7.2? That would give me 0.015625 per step. Guess the torque thing would be the only issue...not sure if just keeping things really slow would help with that. I am not going to be doing any cutting while the stepper in question is active...basically the work would get spun to a point and the spindle will pocket a hole. I plan to have a clamp that gets set during each pocket, so the only force on the stepper will be when it is positioning the work...

thanks,
Howie

[3imoh]

the 7.2 I have is an alpha motor.

-Howie

[richards]

Howie,
Search the forum for posts from Dirk Dunham and Pat Fulghum that describe their indexers that they built using PK296A2A-SGxx motors, Gecko G203v stepper drivers, power supply and standard Shopbot Alpha series controller. The electronics, depending on your power supply, will cost about $500 to $600. Other than that, you'll need a Harbor Frieght (or similar) lathe for another $200.

The PK296A2A-SGxx motor can easily be used if you don't mind tinkering with your machine. I tested the electronics on my PRT-Alpha and had great success.

[Brady Watson]

Mike,
If he already has an ALPHA 7.2:1 motor & driver, why would he downgrade (and spend more $$$) for a Gecko/PK296 combo?

-B

[richards]

Brady,
He's planning on routing a 44" disk. He may need more reduction than the 7.2:1 gearbox offers. There certainly nothing wrong with using the Alpha motor, but it seems like a shame to use a $1,500 motor/driver and then spend even more to add a secondary stage when he can use a single-stage PK series motor with 36:1 gearbox, which would cost $1,000 less than using the Alpha 7.2:1 w/additional seond state.

[Brady Watson]

OK, I got it now. I figured if he already owns the 7.2 motor and driver that for under $100 he can make a nice belt reduction unit and be all set. A couple cogged pulleys, a belt and a motor mount are all that are really needed. Either way will get the job done...My 10:1 Alpha indexer now sports a 3:1 reduction for an effective overall of 30:1.

-B

[beacon14]

What about this approach? Make a large geared faceplate for the lathe, then drive the smaller gear with the motor.

495

[Brady Watson]

It's a great approach - except for the fact that finding a ring gear that large is pretty tough (and not cheap if you did), unless you make it yourself...and what are you going to make it out of - and how much accuracy do you need?

It *may* be possible to use a non-synchronous belt if you had enough tension on it, but non-sync belts slip, and chains 'jump' every so often losing sync.

-B

[3imoh]

Does anyone have the oriental motors model number of the 7.2 geared combo that the PRS machines use? I am trying to track it down on the OM site to look at torque specs, but am not sure which one it is. Not near my machine right now...

BTW, here are a couple of links for folks that might be interested...one is the flange mount I have been trying to find...they are actually used as shaft supports, but they look like they would work:

http://fa.misumiusa.com/gwos/catalog/catalog_list_pc050.aspx?CATALOG_ID=0001&CATEGORY_I D=002

The other thing is what is called a "helical beam coupler". It is sort of like a flexible shaft coupling but allows for a zero backlash setup. Might be a good option for people looking to mount steppers that need to deal with a small amount of misalignment:

http://www.heli-cal.com/Html/Products/prod01.htm

thanks,
Howie

[Brady Watson]

They are similar to the AS98MSE-T7.2 model. They put out 79 inch pounds or 1264 ounce inches of torque.

-B

[3imoh]

Thanks for all the replies to this...hopefully I am getting closer to figuring this out.

Could someone point me in the right direction to find out how much torque I need for this application...I am a bit lost on calculating this.

Ideally, I would like to direct mount a disk to a motor, but I don't know if that is going to be possible. I am considering a belt drive reduction as well as something along the lines of what David proposed above.

The only purpose of the stepper will be to truly index the disk. IOW, the only force on the stepper will be the mass of the disk itself. When any cuts are made, I will be clamping the disk solid to the fixture, so the indexing stepper will not be trying to counteract any cutting forces.

speed of rotation is not that important...1-2 rpm is fine.

just for arguments sake, lets say I have a stepper motor mounted with the shaft horizontal. There is a 44 inch disk mounted to this that weighs 20 pounds.

How much torque do I need to start and stop moving this disk? I have seen some torque calculators, but they are more geared towards a simple lever. I am not sure how to take into account the entire mass of the disk...

thanks much for any thoughts,
Howie

[Brady Watson]

The biggest concern is the overhung weight on the end of the shaft of that motor. You'll need something to take the weight off of the shaft or you'll wipe out the bearings on the motor in a hurry.

If the motor's only job is to index a position before being clamped solid to prevent movement, then you don't need a motor at all. Just make yourself an indexing wheel, with as many increments that you may need. The simplest would be to drill a series of holes in a circular array around the disk and use a complimentary bar or rod to lock it into place. Engrave each index with the degree it corresponds to and you're all set. No motor. No gear reduction. No tricky calculations. No nonsense.

-B

[3imoh]

Thanks Brady-

That was V1.0 :-)

I have a working system based on what you describe...aluminum plate with indexing holes and a spring loaded pin.

The issue are:
1) There are quite a few pockets on each disk, and I have to sit there to index the jig for each one.

2) I now looking at many varying diameters (44" would be the largest) and pocket positions, and would like to edit a program instead of building a new fixture plate for each one...

I am leaning towards a simple belt reduction that would allow me to build up a shaft with bearings that would keep the weight off the stepper. Was hoping to direct mount things, but it might just not be possible...

[pfulghum]

Howie,

Per our phone conversation...

Here is a link to the 3:1 gear drive that Mike Richards spearheaded and that Dirk Dunham uses.

They run a drive pulley (14mm drive shaft) to another pulley on a 1/2" axle.

http://www.talkshopbot.com/forum/show.cgi?tpc=312&post=39324#POST39324

-- pat

[Brady Watson]

You couldn't do something like this then?


496

Too easy, isn't it?




-B

[3imoh]

Brady-

That is similar to what I have now...but the hole spacing may be varying as well. I guess I should have put more emphasis on this part:

"I have to sit there to index the jig for each one."

yup...I am being lazy. I prefer to call it "efficient" though. Sounds better...though that doesn't fool my wife.

I am really hoping to be able to go work on something else while the bot does it's thing...

-Howie

[Brady Watson]

Automation sure beats manual indexing, no doubt. You need either a motor with enough torque to resist deflection when cutting or a motor that has a brake, plus a means to control that brake. I know you can get an Alpha motor with brake, but not sure what is involved with actuating it.

The path of least resistance might be to make a compound belt reduction using two 3:1 setups like Pat mentions. This will give you an effective overall gear reduction of about 65:1. Since you have a large radius to play with, you can just put the gear/pulleys inline. This will give you about 11,000 ounce inches of torque. That should be prenty


-B

[eric_schumacher]

More complex, but a worm gear might give some advantages in the area of locking.

[pfulghum]

One more thing worth noting...

The 7.2 alpha will spin 100X faster than a 7.2 PK motor. Look at the specs.

Take the 7.2 Alpha through a couple of 3:1 belt drives and give it a whirl. It will cost you about $125 in parts to experiment.

-- pat