Tramming the Mills

[platypus20]

A couple of customers of mine, showed me a easy and quick way to tram the head of the milling machine. One of them is an aerospace contractor and the other is a sub-contractor to the first one. They mount a brake rotor on the mill table and then using a simple indicator bracket sweep the surface of the rotor, which gives them a smooth surface to work with. They said if you have any doubts, rotate the rotor 90 degrees and rerun the test. I made the bracket out of 1/2" shafting, drilled and tapped it to hold the indicator. I then removed the vise and mounted the rotor and bolted it down. I installed the indicator and trammed the mill head. Rotated the rotor then reran the tests. Remounted the vise and trammed it in.

1 - the bracket
2 - the indicator
3 - back view
4 - front view


jack

[platypus20]

5 - tramming the mill head, using the rotor
6 - closer view
7 - sweeping to the back
8 - tramming the vise


Jack

[Bearcar1]

An interesting method of tramming the head, how is that you are certain the brake disc is perfectly flat? Of course if it were to be even slightly warped or have one thicker side than the other, that error would affect the accuracy of the procedure.


Jim B.

[platypus20]

Thats why they say to rotate the rotor 90 degrees, and recheck, if its off, the readings will be different.

jack

[Twmaster]

For those of us with smaller mills a the inner bearing race from a tractor-trailer rig will do the same job. The benefit is they are already close to perfectly parallel so no guessing about error.

Good tip on the brake rotor.

[Yorkshireman]

I beg to differ, with respect to the Brake Disk on the milling table.
Any good car mechanic will tell, that brake disks should not be trued up on a lathe, as the brake disks by design must have a tiny runout or wobble, 5 thou, say. On a perfect plane the brake pads would seize up. So using a brake disk like this would NOT put the mill into a true position.

I do use a similar approach though: my plate is a sheet of flaaat 10 mm glas. Works fine for me.

Johannes

[platypus20]

Maybe what you say is true, maybe it isn't perfect, but I find it hard to believe a major military aerospace contractor would use it as their shop procedure, if it is a flawed process.

jack

[cedge]

Jack
Tramming is one of those subjects that seems to bring out the worst in machinists. Everyone has their own way to do it and most simply can't conceive of anyone being dumb enough to do it any other way. My homebuilt Dual Dial Indicator Tram Tool almost started a war when I shared it on one board.  I learned that I was the village idiot.... but hey....  I'm an idiot with one damned well trammed mill.....(grin).

The 90° rotation trick will tell the tale, as will the dial test indicator as it travels around the rotor surface. Bottom line.... if it works.... it works. No need to get into any "only one right way" arguments.

Steve

[Powder Keg]

What Steve said.

But..... I just use the table.