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View Full Version : Stepper motor coupler for Sherline/Denford?



DICKEYBIRD
09-08-2010, 11:57 AM
My little MicroMill is missing the X-axis stepper motor coupling. I contacted the nice lady at Sherline but their couplers are different than what came on mine. Anybody know where to source one of these at a reasonably price?

The ones I saw on the bay aren't the same but look easy to make. Anybody ever made one?

http://i57.photobucket.com/albums/g227/DBAviation/SherlineCoupler.jpg

Evan
09-08-2010, 12:07 PM
Since I already own a piece of this project I may as well own some more. :D

Will this do? It's 5/16 shaft size and you probably need 1/4" but I am sure you can figure out how to make a sleeve or two. I can have it in the mail today.

http://ixian.ca/pics7/coupling.jpg

gary hart
09-08-2010, 12:53 PM
Have made them but didn't take notes or pictures.

Guessing how it was done. Take shaft longer then needed.
Drill and ream for shaft size.
Bore out in center where saw cuts will be in case shafts extend in this area.
Make a wood fixture for the vertical band saw table that will allow saw cut to only go to less then center of the od, just far enough to reach center hole. Fixture is at an angle that is the helix angle of the "thread" you want to cut. Sketch shows wood elevated on one end but what I used was flat board with back fence stop and twisted to helix angle and clamped to saw table.
Run the rod into the saw blade and to the stop fence on your wood jig.
Holding the end of the rod that extends past the wood fixture slowly let the saw turn the rod in the helix cut that it wants to make.

http://img.photobucket.com/albums/0903/ghart3/cnc%20indexer/bandsawcoupler.jpg

Hardest part was making slit for clamping onto shaft.
Drill and tap for set screws would be lot easier.
Picture on one that i made for a stepper motor to indexer.


http://img.photobucket.com/albums/0903/ghart3/cnc%20indexer/Stepperadaptercoupler.jpg

DICKEYBIRD
09-08-2010, 01:17 PM
Thanks yet again Evan.:D It's definitely 1/4" shaft size and yes a couple sleeves will be no problem. There are some overall size limitations though. Can you slap a caliper across the O.D. and length please? I'll check when I get back home from work tonight and see if it'll fit.

Gary I've saved your post and pics in my CNC stuff folder. That's a great solution! Not quite as painless as Evan's though.;)

ps: Evan you're plum dangerous with Paint Sho Pro!:eek:

Evan
09-08-2010, 04:13 PM
It is 1.123" x 1.123" Nominal 1 1/8"

MaxHeadRoom
09-08-2010, 05:06 PM
Word of advice, do not use aluminum helical on stepper or servo, use the Stainless version, for what it cost they are not that expensive from a Helical Coupling Co. supplier.
Aluminum can require replacing frequently depending on torque etc.
Max.

Too_Many_Tools
09-08-2010, 07:30 PM
Word of advice, do not use aluminum helical on stepper or servo, use the Stainless version, for what it cost they are not that expensive from a Helical Coupling Co. supplier.
Aluminum can require replacing frequently depending on torque etc.
Max.


Correct.

Hint...if you write a nice letter to the manufacturer they will send you a sample of what you need.

TMT

Evan
09-08-2010, 07:32 PM
You can pick up the entire machine with the finger of one hand. I don't think it will be over powering an aluminum coupler.

DICKEYBIRD
09-08-2010, 09:23 PM
I don't think it will be over powering an aluminum coupler.Ditto. I think the mill weighs 25 - 30 lbs. dripping wet and the stepper motors are rated @ 180 oz/in torque.

Anyhoo, Evan it looks like your coupler will work with minor mods. PM will be sent, thanks!

Evan
09-08-2010, 09:27 PM
I will mail it tommorrow then. Happy to be of service.

whitis
09-08-2010, 10:00 PM
Yes, the sherline couplers are rather unusual. They put a cone/taper on the end of the lead screw.

These general types of couplers are off the shelf items that you can find at the usual industrial parts distributors or by doing a froogle search on "helical shaft coupler". They can be had for around $20.

Looks like Evan has you covered but others will find themselves in a similar situation.

Long ago, I made a rigid version out of brass for the Z axis on my sherline:
http://i369.photobucket.com/albums/oo135/mwhitis/coupling.jpg
At the time, I was using old beefy steppers that had really good bearings and using the motor bearings provided zero backlash; most modern steppers can't handle this. Note that the flat for the screws is weak and a stress fracture did develop on the inside corner from the force required to clamp the coupling - a counterbore is better. But if you have flats on your shafts, a set screw into the flat is better. The clamp type require some rather severe forces to bend the metal.

The flexible couplings are made the same way but with more slits.

An alternative to the spiral cut is a series of cuts on opposite sides almost half the way through with a slitting saw, rotating the coupler 90 degrees between pairs of slits. You need at least 4 pairs of slits. Leave a gap in the middle between the first two and last two slits to allow greater flex. You don't see these as much now; I think once you are set up, the helical ones can be cranked out a little faster because once the cut is started you are removing a consistent amount of metal. You should be able to make this on the mill with a slitting saw even with one axis out of commission.
slit
rotate 180
slit
translate
rotate 90
slit
rotate 180
slit
translate (move further if you have room)
rotate 90
slit
rotate 180
slit
translate
rotate 90
slit
rotate 180
slit
The slits can also be side by side and go deeper.
http://www.couplingsdirect.com/pdf/Slit_type_Flexible_Couplings.pdf

If you have a CNC rotary table, you can cut the spiral with a slitting saw even with one axis down. Mount the part with the axis of rotation vertical on the rotary table (flat on the bed), tilt the milling head to the correct angle, and program the machine to translate in Z while rotating the table.
Use the X axis for your entry/exit move or to control depth of cut if you don't want to cut full depth in one pass.

Slitting saw holder:
http://www.sherline.com/3065pg.htm
You can use a bandsaw for either type if you don't have a slitting saw.

There are tradeoffs between torsional stiffness and the amount of misalignment a coupling will tolerate.

You can also get the sherline mounts, coupler, lead screw, and drilling guide for somewhere around $100. It isn't listed in the catalog as a single axis kit but the nice lady's who handle orders there actually understand their products enough to tell you what parts you need.

Many types of flexible couplings are shown here:
https://sdp-si.com/eStore/Direct.asp?Exp1=29&CP=Couplings.htm

DICKEYBIRD
09-09-2010, 08:24 AM
Thanks whitis for all the very good good info. Mine is an old (1996) Denford conversion of the Sherline and doesn't have a taper on the leadscrews.

I'm glad I didn't complete the order for one of their couplers 'cuz it wouldn't have fit! From the correspondence I had with Kat at Sherline, I'll bet a return would have been easy-peasy. Good folks there.:)