Shopsmith Forums

Back lash!

With a quick/strong speed error response, the presence of backlash causes rapid back and forth corrections which I believe we are hearing.

Due to the very rapid acceleration(and deceleration) of the pulsed motor, the set screws MUST be very secure to prevent back lash. This has been revealed several times since the introduction of the PP motor.

The PP motor is insidious in that it 'bangs' both directions at the backlash limits.

I do not think the quill is providing any significant back lash. The three internal pulleys are the most likely source. Put motor pulley at he top of that list.

JPG wrote:Back lash!

With a quick/strong speed error response, the presence of backlash causes rapid back and forth corrections which I believe we are hearing.

Due to the very rapid acceleration(and deceleration) of the pulsed motor, the set screws MUST be very secure to prevent back lash. This has been revealed several times since the introduction of the PP motor.

The PP motor is insidious in that it 'bangs' both directions at the backlash limits.

I do not think the quill is providing any significant back lash. The three internal pulleys are the most likely source. Put motor pulley at he top of that list.

JPG,

So interesting. Thanks for the explanation and the emphasis on tight set screws. Can't wait to get out there and check it out.

Not sure what you mean by "quick/strong speed error response".

thanks,

hal

The stepping motor's speed is controlled by varying pulse duration and 'polarity'. The PP motor with extremely strong internal magnets responds to those pulses very rapidly thus accelerating/decelerating at a very rapid rate. Add to that the torque involved and you have quick/strong.

The speed of the motor is sensed constantly(very rapidly looked at) and the power pulses are altered so as to maintain fairly constant speed. The greater the speed 'error' the greater the correction response. Backlash adds a potential time delay to observation of the results of the corrections and causes hunting(back and forth seeking desired speed).

An over simplification, but I hope you get the idea.

IF you determine that a set screw IS loose make sure the set screw is tightened at the mid point of the backlash(similar to rocking an arbor as one tightens the quill set screw). OHHHHHH have thee checked thy face plate set screw and workpiece to faceplate attachment?

hfmann wrote:oooh - that sounds like an intense operation. I'll save that for last. Not even sure how to do it. hal

Not an intense operation at all. Here's a quick and simple video on how to do it.

[youtube]https://www.youtube.com/watch?v=3ZF1xvg6-NY[/youtube]

This procedure is the same for a conventional headstock, and the Power Pro headstock.

Like I said before, I highly doubt your quill is the problem, but it never hurts to do a thorough diagnostic check of all the mechanical parts, especially if they're easy and quick to check.

hfmann wrote:

Chad wrote: Couldn't hurt to remove the quill and check the bearings, and for a bent quill shaft as well, even though I highly doubt the quill is the problem.

Hi Chad,

oooh - that sounds like an intense operation. I'll save that for last. Not even sure how to do it.

Thanks for the idea.

hal

Probably easier than working on the motor. This video goes over the process: http://www.shopsmithacademy.com/SS_Arch ... rn_Pt4.htm

Here is a short video on how to disassemble your quill:



And here are a couple short videos on bent quill shafts:

Thanks Chad. Always helpful to get to see the actual process.

hal

JPG wrote: IF you determine that a set screw IS loose make sure the set screw is tightened at the mid point of the backlash(similar to rocking an arbor as one tightens the quill set screw). OHHHHHH have thee checked thy face plate set screw and workpiece to faceplate attachment?

thanks JPG - Interesting explanation.

and yes - I've been careful about tight faceplate set screw and attachment. My workpiece to faceplate attachment feels so much better since I switched to 6" faceplate (where possible) 9 #12 hex head metal work screws.

to you earlier comment "The three internal pulleys are the most likely source." I looked at the xploded parts list (attached) and couldn't find three pulleys. Maybe i'tll be obvious once I open it up.

thanks,

hal

Motor shaft pulley
Idler shaft pulley
Drive sleeve pulley

two belts motor-idler-drive

Thanks JPG.

hal