Tramming my PM-950V mill....

[Firstgear]

Got the X axis done, +/-17” from the center, I have just under 0.001 difference between those two outer points. Talk about sensitive! Felt like a ping pong match going back and forth....

Next up, Y axis!

 

[Firstgear]

Well, if I had to choose between lucky and good, I always take lucky! Luck was on my side....front to back on the 9” table was hardly different.....if I was to bet, less than 0.0005

Now I need to put my more sensitive dial indicator on it.....let’s just see what that says.....well, it says 0.001 which is good enough since I am not making Space X parts......

 

[Bob Korves]

If you are trying to make the length of travel in both directions exactly equal, well, that does not do much for you that is actually usable. Now that you have done it, mark the turret to column interface in some way so you can quickly and easily return to it someday if you move the turret for one reason or another. Where the head is relative to the table does not change accuracy anywhere, because there is no feeding of the ram for making cuts. Congratulations on the .001 and .0005" centering, but within half an inch would be suitable for 99.99% of jobs.

 

[Firstgear]

If you are trying to make the length of travel in both directions exactly equal, well, that does not do much for you that is actually usable. Now that you have done it, mark the turret to column interface in some way so you can quickly and easily return to it someday if you move the turret for one reason or another. Where the head is relative to the table does not change accuracy anywhere, because there is no feeding of the ram for making cuts. Congratulations on the .001 and .0005" centering, but within half an inch would be suitable for 99.99% of jobs.

I probably wasn’t clear....I was tramming the unit in the X and Y directions. The X was trammed over a total distance of 34”. Hence 17” on either side...I have no idea if the bed was centered,it was probably close, but I was tramming the machine.....does that make sense?

 

[darkzero]

Wow, I've never heard anyone tram over a distance of 34" (for these size mills). It's unnecessary & won't make part accuracy any better. Hope whatever you used was pretty stout & didn't have excessive sag. But if it works for you all good, just saying it's really not necessary going to that extreme.

 

[Bob Korves]

It sounds like you were checking for variations in height from the spindle or head to the table along the entire X and Y axes travel by moving the table? If so, that is a good test, but not necessarily tramming. Another issue is that if the indicator is attached to the spindle or head, and the table traversed, you could have a situation where as the table travels, it sags towards the overhanging end, but you would not necessarily find the discrepancy at the indicator. You can produce a convex part that indicates perfectly to the head. That is a common problem with milling machines and surface grinders -- an even and significant curve in the table travel caused by table overhang wear or looseness makes little or no movement of the indicator. If the mill is new or nearly new, it may not have that issue, depending... My old surface grinder has that issue, to a minor extent, for sure.

 

[Firstgear]

It sounds like you were checking for variations in height from the spindle or head to the table along the entire X and Y axes travel by moving the table? If so, that is a good test, but not necessarily tramming. Another issue is that if the indicator is attached to the spindle or head, and the table traversed, you could have a situation where as the table travels, it sags towards the overhanging end, but you would not necessarily find the discrepancy at the indicator. You can produce a convex part that indicates perfectly to the head. That is a common problem with milling machines and surface grinders -- an even and significant curve in the table travel caused by table overhang wear or looseness makes little or no movement of the indicator. If the mill is new or nearly new, it may not have that issue, depending... My old surface grinder has that issue, to a minor extent, for sure.

X axis - I took an aluminum bar that I had, about 18” long (it’s what I had) and 3/4”x2” wide. 12” from one end I put hole about 1/2” in diameter and then pressed a round bar of steel into the aluminum. On each end in the center I threaded a hole that my dial indicator multi axis adjustable shaft could thread into. I took a 1/2” R8 collet and used that to grab the 1/2” rod and inserted that in the spindle, snugging it up with the drawbar. I mounted my dial indicator on its mounting rod.

I put the mill head in high gear so I could easily rotate the aluminum bar from one side of the bed to the other side and adjusting the head rotation to eliminate variation in height between the two sides. This variation in height of the two ends of the bed relative to each other, I measured to be 0.001”.

Does this make sense?

 

[Firstgear]

Wow, I've never heard anyone tram over a distance of 34" (for these size mills). It's unnecessary & won't make part accuracy any better. Hope whatever you used was pretty stout & didn't have excessive sag. But if it works for you all good, just saying it's really not necessary going to that extreme.

I used what I had and didn’t shorten it hence why it was so long. 12 years ago I was walking through the machine shop at work and they had this pallet of 7061-T6. When I asked what they were doing I was told waiting for the scrap guy to come and give a price and take it. I told them I would take it. Wrote a check and had it loaded into my truck bed.

There was some plate aluminum, 1/4” x 12” x 24” (about 16 plates), 12 of these 3/4”x 2” bars and then some odds and ends. At the time I bought the pieces I wanted them for making parts out of them for my cars. For instance I took one plate and had a friend that owns a shop make me an instrument cluster that was also a steering column mount for my Model A street rod. Now I am building a restomod 1963 Corvette Split Window and there are lots of custom things ?I need for the build. It was because of the Split Window that I bought the mill and lathe. I kept going to my friend who owns a machine shop for parts to be made. I decided I needed to only go there when I had something difficult to make.

 

[Bob Korves]

Yep, you actually trammed it that wide! OK, fine. Just a bit out of the ordinary...

 

[Firstgear]

Yep, you actually trammed it that wide! OK, fine. Just a bit out of the ordinary...

The owners manual indicated maybe a total span of 6 or 10 inches....I get why they said that....it’s very sensitive to even a very slight change...to be honest, it was a PIA!