View Full Version : RFQ: Need ideas (or someone to make) a widget to couple motor shaft to M8/M10 threaded rod

16-04-2013, 11:12 PM
Not really CNC, but hey, it's nice to have a bit of a breather once in a while! (though it is related)

I'm struggling here...I'm making a CNC coil winder (as cheap as chips one with mainly stuff sourced from my box of spares/odds 'n ends), but I no longer have a mini lathe ...else I'd have just tackled this myself.

i need to couple a 1/4" (6.35mm) stepper motor shaft directly to either M8 threaded rod (or M10) threaded rod.

What I'm aiming to emulate is this....


so the idea is to feed enameled copper wire over a helix onto a bobbin ...incidentally, the wire is much much thinner than in the above video (at about 0.15mm->0.2mm dia)...which I think he's exaggerated just to illustrate the method)

The guy in the video used a nylon helix (with what looks like an inner steel core, as bending/deformation would not be good!)...I guess his reasoning is to give a soft 'helix' for the wire to feed over (else there's a risk of the enamel stripping off the copper wire). I've already made a similar effort...I bored M10 threaded rod - but I wasn't very good & it doesn't turn true (there's a fair bit of visible- for want of a better word 'runout' at the end of the helix as it turns!)...that said, it didn't seem to strip the enamel of the copper wire, so I'm not sure it's necessary to go to all the hassle of what the guy has done in the video - also, using nylon would wear out much quicker)

therefore options are...

1. Pay someone to bore out a short piece (15cm) of M10 threaded A2 stainless threaded rod with a 6.35m hole & slide this snugly over the stepper motor shaft.

If not, then my preference is actually to use M8 threaded rod (finer pitch to guide the wire more accurately...also I have a lot of supporting stuff I could use if using M8 vs. M10)

2. Source something like this ALUMINIUM ROUND TUBE 1/2" OD x 1/4" ID x 200mm LONG GRADE 6063 T6 | eBay (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190825075380) & ask someone to make some 6.35mm-> M8 threaded rod couplers from it (therefore just bore out the 6.35mm hole to 7mm & tap with M8 - but I'd need this done accurately, which rules me out!)

3. Buy one of these 'off the shelf' couplers .. 6.35mm x 9.5mm Flex Coupler 1/4" to 3/8" Shaft Coupling | eBay (http://www.ebay.co.uk/itm/6-35mm-x-9-5mm-Flex-Coupler-1-4-to-3-8-Shaft-Coupling-/250896762926?pt=LH_DefaultDomain_0&hash=item3a6a9cc82e) (it's 3/8" which is9.5mm...I could tap that & feed in some M10 threaded rod & then the grub scews would hold). I'm not keen on this idea, because obviously it needs me to accurately tap...past history is not good when it comes to me being accurate/square! Also I've no need for the 'flex' ...in fact I'd rather have a straight metal couple with no flex at all.

Edit: Re option 3....I've actually, just this moment found this coupler - http://www.ebay.co.uk/itm/BR-6-35mm-x-7mm-CNC-Flexible-Coupling-Shaft-Coupler-Encode-Connector-D20-L25-/400394187199?pt=LH_DefaultDomain_3&hash=item5d395a71bf ....6.35mm->7mm coupler) & because the 7mm hole is pre-drilled, even I ought to be able to tap it to M8! This is a good late contender!

Top tips to solve my dilemna warmly welcomed.

John S
16-04-2013, 11:34 PM
So you want a bit of threaded rod with a hole in the end for a 1/4" stepper shaft ?

Ok how long do you actually need, what thread and what material.
it's quicker to actually make what you want than piss about bodging up.

PM me the details.

17-04-2013, 12:51 AM
PM'ed :-)

17-04-2013, 01:12 AM
I would stick with the nylon tread as it will protect the wire, the thread is only a very crude ( but effective) traverse feed. It might be worth making it over long and supporting it on both ends, that will solve the run out and give you the option to wind 3 pickups in one go.

Started a winder project a while ago but didn't get to cnc,ing it. Used an aurduino to set motor speed and count coils. Have you looked at ink jet printers? They often have small steppers connected to plastic thread. Might save a bit of work.

Off topic but have you thought about wire tension? From what i remember it is fairly critical to the sound and therefore repeatability.

17-04-2013, 08:06 AM
BF-D25L34 Flexible Coupling (http://www.zappautomation.co.uk/en/flexible-couplings/282-bf-d25l34-flexible-coupling.html)

17-04-2013, 08:11 AM
I did something similar where i drilled the hole undersize, put a cross split on the end of the rod. Put the shaft in the end and then used a a long nut and screwed it on tight. For this a 6mm drill maybe ok as there is a bit of slop in the nut anyway?

17-04-2013, 09:10 AM
Ok, firstly thanks to John for his offer to help - I had a moment of doubt late last night & have asked him to hold off while I mull the design over a bit longer.

There are a couple of things I need to address further down the line (not sure I should worry about them now).....

1. Repeatability - I can tell you with a degree of certainty, that aligning 0.15mm wire up at the zero poiint is a pain in the @rse...so I'd like to aim towards a way of automating that (some) form of homing the feed wire (optical perhaps?)
to take the visual guesswork out of this (unless you get the start point right...you end up with an uneven wind)
2. Speed of setting up (sort of related to No1) ....if my latest efforts work...I might need to make a lot - I don't want to get bogged down spending 10 minutes setting everything up!

....but I guess I can worry about those later ....pointless obsessing until I've proved the concept.

John mentioned in PM a couple of ideas re a better version.

A deluxe model would be like this guy has done....


he uses a linear actuator with a syringe attached to it (to feed the wire through) thread discussing here Working on a new winder. . . (http://music-electronics-forum.com/t31799/) ...my needs are slightly different - guitar pickup makers are all winding very hair like thin wire with not so much tension, I'm winding 3x thicker wire under a fair bit of tension (I'd be worried about any syringe needle bending or scratching the enamel off the wire). While we are speaking of deluxe, there's also clanzer who's selling coil winders.... CNC Design Limited - CNC Coil Winder (http://www.ukcnc.info/forums/coilwinder.php) (but I prefer a solution where the main winding motor is a stepper vs a dc motor...I need a lot of torque at lower revs)

Juku...thanks for the link if I'm to go the way of a flexible coupling I think I'd go withe 6.35mm->7mm (which I can tap to M8 thread)

Ross ....I'm coming around to the idea of supporting the end of the threaded rod (perhaps not at the very end, but near the end with some bearings).... indeed here's a recent attempt (my machine isn't strong enough for ali, so I simply use acrylic)...


(just held together loosely to give you a vibe of what I'm thinking of...at least there's a bit more support near the end of the (M8) threaded rod)

for tension, I use the tried & tested two felt washers under tension to feed the wire through

Swarfing...anything that involves me, a drill & accuracy.... can only result in much hilarity & disdain from passing children!

17-04-2013, 10:05 AM
Juku...thanks for the link if I'm to go the way of a flexible coupling I think I'd go withe 6.35mm->7mm (which I can tap to M8 thread)

No need to tap; the 8mm side would squeeze hard enough on a M8 thread -at least 5mm version takes M5 without a problem.

17-04-2013, 11:54 AM
No need to tap; the 8mm side would squeeze hard enough on a M8 thread -at least 5mm version takes M5 without a problem.

Just mulling here ..... whaddaya you all reckon the lesser of two evils would be (from a rod wobble perspective)...

1. Tap a flexible coupl '7mm hole' to M8 & screw the M8 threaded rod in
2. Squeeze an 8mm opening hole down onto M8 threaded rod

17-04-2013, 01:19 PM
Not sure either are very good, probably retaping the flexible is more controllable but not sure how easy that will be to actually do. if you force on to the rod there is a good chance that it will shift to one side as it hits the first part of the thread.

Unfortunately for the kind of precision you need it needs to be turned to ensure it is concentric. I would take John up on his offer and ask for him to turn down a threaded bar with bearings on each end and the last section tuned to 6.35mm so you can use a flexi coupler to the motor.

If its real quick and easy you need then go back to the 10mm and counter bore with 6.35mm and fix to shaft with glue of grubscrew. I have some steppers here that are done the exact same way (except with leadscrews) and they work fine.

17-04-2013, 01:29 PM
....turn down a threaded bar with bearings on each end and the last section tuned to 6.35mm so you can use a flexi coupler to the motor.

The problem with a bearing on both ends of the threaded rod is one of access...I need to get my hands in/out a lot (to wind the copper wire on to the main bobbin etc)...this is why if you look at my last photo (of my 'loosely lashed together up' design), I supported the threaded rod a few centimetres in from the end of the rod with a small bearing ....that keeps everything nice & clear/open for ease of access (& it's also easier to thread the copper wire under an open ended bit of threaded rod)

17-04-2013, 07:35 PM
The problem with a bearing on both ends of the threaded rod is one of access...

The bearings don't have to be at the very ends. You just need the shaft constrained by two bearings to keep it concentric, then the flexible coupling can do it's job and take out any minor alignment problems. keep the arrangement you have but add another support plate and bearing after the coupling, as you have it at the moment the threaded bar will pivot about the middle bearing and exaggerate any alignment issues.

Have you thought about using a hex bolt and cutting the head off? that way the shank could act as a shaft for the bearings and having a solid round end would be better for forcing on a under sized flex mount.