PM935TV drawbar tune-up

A

Alan H.

Forum Guest
Register Today
As part of an inspection and cleanup on my mill, I discovered the drawbar threaded end was slightly worn (operator error caused). Since they are a consumable I took measurements so I could make a spare sometime. I then tuned it up a bit so I could put it back.

The shaft part of the bar was nice and true but the large diameter/nut end is slightly canted relative to the shaft.

As a result of this canted big end, the shoulder of the bar was not perfectly true to the long shaft. So I trued it up, made space for a washer, and also trimmed and beveled the threaded end removing a bit of wear/damage. The bar's shoulder also now sits on top of a new bronze washer to prevent any wear to top of the spindle it rides.

I suspect it is likely rare to find a really straight and true drawbar. It may be totally irrelevant since they are mighty flexible and a bit of a crude device anyway. So yeap, I know this may be a bit of perfectionism showing but what the heck, that's how I roll sometimes. I even coated some of the bearing surfaces with colloidal graphite!

Threaded end trimmed, beveled and chased:

trimmed, beveled and chased the threads.jpg


Truing the shoulder:

Squaring the seat to the rod.jpg


Bronze washer coming off the lathe:

making a bushing from bronze.jpg


Graphite coating being daubed on before it was reinstalled:

coating with graphite suspension.jpg


The new washer and shoulder trued up:

washer and bar ready to go.jpg


The tuned up bar (before graphiting):

bar with new washer.jpg
 
I have now tested out another option/alternative to the stock drawbar.

McMaster sells a bar that works and that is made in the USA.

The bar is intended for a Lagun variable speed mill. The rod end is a perfect length but the hex end is a bit long. Of course that is easily remedied by trimming it down. I trimmed it and then crowned the hex so my power drawbar socket would mate easily. The threaded end is long enough to trim a time or two to renew it. The bar is very well made - nice and straight and includes a washer.

Here's the hex end trimmed, the washer, and a shot of the manufacturer's label:

IMG_20180218_115345.jpg


Crowned:
IMG_20180218_115146.jpg


I trimmed it to let it protrude a little higher than the stock bar. I can now easily manually start the threads if needed and then follow up with power drawbar drive I have.
IMG_20180221_094751.jpg


IMG_20180218_115014.jpg


IMG_20180218_120106.jpg
 
Back
Top