Need Help!- Adapting original pulleys to nema 34 steppers

[CNCISME]

I am retrofitting a boss 5 mill and prefer to use the original 5/8 inch bore axis drive pulleys on nema 34 steppers with 1/2 inch shaft. The shafts have a flat place ground to I suppose accommodate set screws for securing pulley to shaft.

Is it common to attach drive pulleys to steppers/servos with set screws ? The original pulleys had a keyed shaft and a taper-lock set up. Set screws would be an easy solution but would it be a good solution. This topic has been discussed on other threads but I am looking for some fresh input. I plan on machining out the center of the taper lock and attaching it to a hub that I will make to fit the shaft. Question is how to secure hub to shaft !

Anyone been there done that?

[mactec54]

CNCISME

The set screw are not going to be enough to hold the pulleys for that machine, they most likely will work for a while.

You can get a 1/2" taper lock bush for the pulleys you have, & you could also cut a key in your motor shaft if you can't get motors with a key

[CNCISME]

Thanks Mactec....
I bought a never used Logitrol 3 axis retrofit kit on ebay and I also bought the BOSS 5 rigid head mill from the same man. The steppers are NEMA 34 1840 in.oz motors. My belt pulley ratio is 1:1 and I am driving approx. 2 inch, 2 1/2 inch, and 4 inch pulleys.

So why do they mill a flat on the stepper shafts if the torque is so much that the set screws will not hold ???

My plan was to remove the taper-lock and bore the pulleys out to a larger diameter to remove the tapered bore. Then I was going to make a bushing to fit and then make a bolt on flange that would bolt on to the end of the bushing and and also bolt on to the side of the pulley to keep the pulley from spinning on the bushing.

Sooooooooooo.... looks like I need a better idear

[CNCISME]

Hey Mactec...

Using keyless bushings which taper lock without need of a key has been discussed on other threads here. Do you know of anyone using them successfully

[mactec54]

CNCISME

You could try the taper locks, the Z would be ok for sure as there is not much load on it, but I would not say that for the X & Y axes, as I have said before, there are different types of taper lock that work better than others, your is one of the one that don't work so good without a key

The pulleys that were on there had keys for a reason

[CNCISME]

I agree Mactec ... the keyed shaft is there for a reason. Perhaps a keyless connection will work but I need to investigate because i want a fail proof retrofit. I got the keyless idea from this thread titled "Amae's Bridgeport Series 1 Boss 3 retrofit" ..... this thread was never completed so I do not know if these ideas were successful. I have not yet found a good example of NEMA 34's adapted to a BOSS machine
http://www.cnczone.com/forums/showth...ight=boss+nema

One man who contributed to this thread adapted using NEMA 34 to 42 flange adapter and shaft extenders with 5/8 inch diameter.... but he did not like the conversion and went back to the original NEMA 42 steppers.

[mactec54]

CNCISME

The keyless taper locks he was using may work ok on your motors, the only problem that you have is you have a flat milled on your motor shaft, so that type won't get a good grip on the shaft & it will slip, they need a full round shaft to work & even then under a heavy load they do slip

[CNCISME]

Mactec

So what do I do now? Would set screws and keyed shaft work successfully? I do not want to be a cnc cobbler ..... I want to make a never fail kind of retrofit here.

The rex stepper manufacturer had a plan when they milled the flat..... so what was their plan ??? .... to secure the pulleys ?????

[Quentinlong]

Originally Posted by CNCISME Mactec So what do I do now? Would set screws and keyed shaft work successfully? I do not want to be a cnc cobbler ..... I want to make a never fail kind of retrofit here. The rex stepper manufacturer had a plan when they milled the flat..... so what was their plan ??? .... to secure the pulleys ?????

I had the same dilemma a while back, albeit on a benchtop mill.
The best solution I found was to mill the bore in the pulley to match the profile of the motor shaft. The motor shart on mine had 2 flats, so the bore hole in the pulley ended up looking like a teardrop.
I finished it off with a grub screw through the hub onto each flat, just as a bit of security.

[CNCISME]

Quentinlong

Thanks for your input .... I also had thought of that.... but .....
my ball screw on the x axis is belt driven with a 1;1 ratio and has a 5 tpi pitch so takes considerable torque to drag the weight of the table plus up to 300 lbs of payload in rapid. My hub will be made of steel and the flat on the 1/2 inch shaft is 1 inch long and 1/4 inch wide. I can interpolate a bore with a flat side but the endmill is going to be around 1/4 inch to get much of a flat. Also boring 1 inch deep with a 1/4 inch endmill would seem to be pushing the limits.... I am not an experienced machinist ....I am just a man who completed 5 months of cnc training last year and have not found work in a shop yet.

But thanks for you input and I will let others judge if your idea will work successfully in this application

[CNCISME]

1979 BOSS 5 Bridgeport. Ways are decent. Includes 3 axis Logitrol retrofit kit. Inquire within

[CNCISME]

Quentinlong

I did some thinking .... you can not interpolate an inside corner without leaving a radius..... so I would need to further machine the shaft to match the profile of the hole.

I will contact the seller to see if he requested motors with flat on shaft when he ordered them from Logitrol. I doubt if he did.