PM932- PDF Gearhead Tilting Modification.

[Ratz]

Adjustment/tramming of the gearhead after tilting for milling operation (or procedure for oil change as described in owners manual) is less than desirable IMHO.</SPAN>

I would like to share my modification with all other owners of PM932 and other mills of similar design. Please note that this undertaking may void your warranty so I would like to caution anyone to proceed at their own risk.</SPAN>

Pictures in my other post will show you where you are drilling to.</SPAN>

http://www.hobby-machinist.com/showthread.php?t=22275</SPAN>

Tilting the head is seldom used in my world, as when milling a small part I use tilting table. When faced with larger part tilting the gearhead is desirable.</SPAN>

When returning gearhead back and/or tramming the head before that critical job I found the task of this precise adjustment frustrating.</SPAN>

Pictures will explain this simple device in greater detail.</SPAN>

I fabricated an “H” bracket from 2” x 3/8” 316 stainless bar (not from choice but found some lying around the shop). Picture of one bracket is for reference/concept as I managed to screw up the fist one. I made the ends too short and bolts lined up with bolts holding down gearhead cover.</SPAN>

New and usable bracket was snug and pushed against the gear head. Bolts holding the bracket to gearhead are 5/16” NC and are tapped right through the casting. Since I had the cover off I was not too concerned drilling into something crucial. I used grease first on 1/8” drill and then on 9/32” drill bit to make the filings stick to the drill bit. I used grease on the tap for the same reason. I found being about in the middle of the recess for the adjusting nut is about right location.</SPAN>

I then supported the whole gearhead on blocks and moved it out of the way with help of the table. Once I gained access to the slide, I installed the metal block to take the force of 1/2” NF threaded rod.</SPAN>

While doing this I discovered that there was no grease whatsoever on the swivel and bolts. I ran a thread chaser on the bolts and liberally applied Red N Tacky #2 grease. Moved the gearhead back into position and finger tightened the nuts. Gearhead turned relatively easy with help of grease application. I made the metal block on the slide too high and therefore at this time I am unable to turn the head 90 degrees so I will have to cut it down.</SPAN>

I cut the 1/2” threaded rod to length and welded nuts on the end. I used the home made “T” bar with two gauges for rough setup and then used finer gauge on a spindle bracket with 8.5” sweep for fine adjustment.

For anyone interested. To adjust the nod of the gearhead, I had some plastic shims from Little Machine Shop. I used 0.006” shim under the two front bolt of the dove tail column. This was done couple of month ago. I have since purchased brass shims from Enco, but never changed the plastic ones. They appear to be standing up to the task quite well.



</SPAN>

 

[Smudgemo]

This is a very useful improvement for this sort of machine. I did this type of mod on the Grizzly G0704 I had, and it made tramming so much less difficult. Mine was just a quickie-job using what I had on hand, but it also worked very well. Even with the most care I could muster, tightening the head bolts while tramming would knock mine out every time. Once installed, that nonsense stopped.



I'll also throw out there that sweeping a large bearing race of high quality laying flat on the table is easier than bridging the slots with a feeler gauge. You can get a US made Timken from ebay for under $10. Get something 5"+ and you can sweep in 360* moving nothing but the spindle. Just a thought.

I ditched the mill but kept the race.



-Ryan

 

[jbolt]

Nicely done! This is on "list" of things todo as soon as I get the power drawbar completed.

How much "nod" do you have? I have my Z dovetail snug but not too tight since I converted to CNC. It took 0.016" of shims to true the spindle on my 932.

Jay

 

[Ray C]

All,

Here's a rough outline of a simple, removable tramming aid that temporarily clamps on with a bolt. No drilling/tapping (voiding warranties) in the head needed. Once it's temporarily clamped on, you just use some bolts as a push-pull mechanism.

The bolts in the picture are not shown but the holes indicate their location. Specific dimensions are not shown as the general concept can be used on other mills -and 90% of all mills in this size class use the same method of head attachment and swivel. Since it's such a poor design, it was adopted on the vast majority of the mills we use. Interestingly enough, I'm now in the process of purchasing $100,000.00 CNC mill -and it uses the same design; albeit, with a few more annoying bolts to deal with.

 

[mgalusha]

Very nicely done. I too did something similar on my '45 clone, makes tramming much quicker and precise.

 

[Ratz]

This is a very useful improvement for this sort of machine. I did this type of mod on the Grizzly G0704 I had, and it made tramming so much less difficult. Mine was just a quickie-job using what I had on hand, but it also worked very well. Even with the most care I could muster, tightening the head bolts while tramming would knock mine out every time. Once installed, that nonsense stopped.


I'll also throw out there that sweeping a large bearing race of high quality laying flat on the table is easier than bridging the slots with a feeler gauge. You can get a US made Timken from ebay for under $10. Get something 5"+ and you can sweep in 360* moving nothing but the spindle. Just a thought.

I ditched the mill but kept the race.


-Ryan

Very nice idea using old bearing race. I will look around for one.

Sometimes I use piece of glass, but not sure how accurate it is since glass is only 1/4".

Feeler gauge is just a habit I acquired to test the gage and feel the gauge if I am running out of travel. Bridging it over "T" slots became a by-product.

Thanks for your input.

Radek

 

[Ratz]

Nicely done! This is on "list" of things todo as soon as I get the power drawbar completed.

How much "nod" do you have? I have my Z dovetail snug but not too tight since I converted to CNC. It took 0.016" of shims to true the spindle on my 932.

Jay

Thanks, I am sure you will be happy with this addition. Just greasing it was a big improvement.

Since nod is adjusted by shims on this mill I will call it fixed. Looking at my own pictures the difference is 0.0003” over the 8.5” span. This small number is pretty well useless for this type of machine, because as soon as it is put to use it will settle with much larger error, as there is too much flexibility and other variations. Even with everythink locked, You can grab the gearhead and see the flexing.

I think perhaps you meant how much tilt my machine has with this device. At present time it is about 35 degrees, but if I cut a chunk off the bracket as in picture below (marked with felt pen), it will go all the way to 90 degrees and all the way upside down if desired.

Cheers,
Radek

 

[catoctin]

.

I'll also throw out there that sweeping a large bearing race of high quality laying flat on the table is easier than bridging the slots with a feeler gauge. You can get a US made Timken from ebay for under $10. Get something 5"+ and you can sweep in 360* moving nothing but the spindle. Just a thought.

I ditched the mill but kept the race.
.

-Ryan

Ryan,
Do you have any idea what this bearing race was originally used for? I did some hunting on ebay and the closes thing I could find were races from truck carrier bearings?

-Joe

 

[John Hasler]

Ryan,
Do you have any idea what this bearing race was originally used for? I did some hunting on ebay and the closes thing I could find were races from truck carrier bearings?

-Joe

Get a disk out of a scrapped hard disk drive. The surfaces are very flat and very parallel. I use an 8" disk but 8" drives are long-obsolete and so rather rare now. If a 5" bearing race would do so would a disk from a 5-1/4" hard drive. Those should be easy to find.

 

[Smudgemo]

Ryan,
Do you have any idea what this bearing race was originally used for? I did some hunting on ebay and the closes thing I could find were races from truck carrier bearings?

-Joe

I don't recall, but probably a truck if I had to take a wild guess. I recall I just looked for a US made Timken race (no bearing) in a size I could use.