The planets are in alignment

[DonInReno]

My darling significant other bought a nice little Wittenstein 75 series 7:1 planetary gear reduction unit as a birthday present!  To be honest I have no idea if this will somehow work in place of big pulleys and extra belts let alone be a better solution, but it's cool and in my hands so we're gonna try!

Nothing in any google searches comes up regarding planetary reduction and sewing machines of any kind, but doesn't it seem reasonable that something like this could make a cleaner way to slow things down?  If anyone's gone down this road it would be interesting to see what worked and what didn't.

Rather than start with a marginal reduction and have to use a really small drive pulley, 7:1 can be sped up easily or kept super slow.  This unit has .866" (22mm) input and output, with the input sleeved to .754" or so.  A different sleeve will need to be whipped up fitting a servo motor and some kind of plate to mate the motor securely.

How noisy are these? The other potential downside is how significant the extra rotational friction is and how it affects manually using the hand wheel. This might be the downfall of the unit since the rubber seals have quite a good grab on the shafts, but it can be spun backwards with about the force it takes to turn over a Juki LU-562 type of machine.

 

 

 

 

 

[Gregg From Keystone Sewing]

Obviously only one way to find out...report back please!

[DonInReno]

Finally a relaxing weekend to play with the reducer!  Since it's usually best to start with easy stuff.  The factory spacer was removed and a little duct tape became a temporary coupling to make sure the initial motor torque could overcome the grip the oil seals have on the input and output shafts - at least with no additional resistance the motor didn't seem to notice the reducer was attached.

Another potential problem was an additional source of noise.  However, these reducers are nearly silent - or at least the motor hum drowned out any sound the planetaries may have made.

The cool part is right off the reducer on the lowest 200 to 500 RPM speed range it's roughly 30 to 70 RPM so even directly coupled to the head 1:1 it's a nice slow granny-gear range, albeit maybe a little too slow.  At 3000 motor RPM's the reducer puts out 410 RPM's - (edit - this is about the speed I like to sew most things at).

The higher the reduction the harder the hand wheel on the sewing machine will be to turn so my gut feeling is the reducer needs a slightly larger pulley than the machine for that reason as well.  

Edited April 14, 2018 by DonInReno

[DonInReno]

A scrap of 1/4" aluminum large enough to mount to the motor that will in turn attach to the factory spacer on the reducer was a whopping $ .40 and a bronze sleeve that will be bored out and pressed on the motor shaft was another $3.

This motor is not in any way bullet proof! Just looking at the thing cracked the fan shroud and the front cover that supports the input bearing is not confidence inspiring - definitely too thin to mount the spacer to, so the four screws holding the bearing retainer in place will also be the attachment points for the 1/4" aluminum plate.  The bearing retainer bore must be cast .003" -.004" larger than the input bearing - at the slightest bearing roughness this is sure to be the end of the motor as the outer bearing race eats and wobbles out the retainer - hopefully it squeals a warning before spinning the bearing.  Having said that there's no reason this motor can't run indefinitely as long as it's not overheated damaging the coils and the sealed ball bearings are replaced at the slightest sign of roughness.  There are no brushes or other moving parts.  

[DonInReno]

To make sense out of these reducers there is a lot of documentation in the 454 page catalog!  Basically I picked up a rather ordinary middle of the road model.

[480volt]

How about a little Loctite red on the bearing when you assemble it to encourage it to stay put?

[DonInReno]

Yes, I think some kind of extra hold on the bearings is a good idea.  I'd like to still be able to pull the covers without having to heat them up to release something like loctite so....IDK.  I'll probably peen the aluminum to close up the bearing recess a little to a stiff slip fit and not worry about it.

 

As for the reducer I picked up, the next one will be a smaller size - the o75 size is rated for about 50 ft-lbs of output torque - much more than required.  The ratios available are 1:3 to 1:100 and 1:5 is probably a better choice as well! Lol

There are literally hundreds of variants of this reducer - many of which would be hard to retrofit, so it's pretty important to at least see the input and output.  

[DonInReno]

The reducer is finally installed, but not in the way originally intended.  Direct connection of the motor shaft to the input of the reducer seemed like a great idea, but it turns into a long awkward looking contraption.

With the Consew CSM1000 the 111w155 with factory hand wheel will sew one stitch per second up to about 30 stitches per second - the speed range I was aiming for.   The biggest downside to this arrangement is the force required to turn the hand wheel by hand - it would be much better to use a bigger hand wheel and bigger output pulley to reduce the reduction a bit.

I wouldn't get another planetary reducer unless a servo with NEMA mounting arrangement could be used to cleanly directly mount the two.  Compared to the typical 3:1 pulley reducer it is more compact, and different, but better I'm not so sure yet. :-)

[DonInReno]

Rather than shifting machines with different bed lengths to the rear of the bed cutout to line up with the speed reducer, I want to easily slide the motor/reducer to where a machine is.  It’s a tall order to use one table for a sailrite clone to a double needle upholstery machine, to a center mounted cylinder arm, to an edge of table mount! Lol   

The 7:1 reducer was just way too slow and 3:1 is popular for a reason.  This little guy is 3:1 and was removed from decommissioned equipment. About $500 new - for $100 I don’t mind if it has .001” extra backlash, but so far it feels nice and tight.  

 

[dikman]

An interesting project, I look forward to seeing how it turns out.