Tramming Results

[Gunney]

I just finished tramming my new mill and I have it down to 0.0008" over 12". It seems to me that should be good enough for most of the projects I'm likely to do, but I'm interested in other opinions. My mill, a Precision Matthews 45M, is a 9x32 bench-type mill with a square dovetailed column. I had to shim the front two bolts that hold the column to the base using 0.001" shim. I'm using a test indicator graduated in 0.0005" attached to an indicol on the quill. As I rotate the spindle, the indicator tip sweeps out a 12" circle (I have to traverse the table fore and aft to keep it under the indicator). I don't have any shim stock smaller than 0.001" (not even sure if I could find any), so to get it any better, I guess I'd have to put some combination of shims under both the front and rear bolts. So what do you think, is 0.0008" close enough, and if not, does anyone have a better suggestion on how to reduce the error?

Thanks,
Patrick

[dp]

It's close enough. I use paper and mylar film for shims on mine.

To get around the traverse issue try this:
http://www.youtube.com/user/spudzwon#p/u/1/ZfioLDhBNBQ

I normally put the brake rotor face on the table but thought this would be easier to see. Brakes are remarkably parallel when new.

[Carld]

Keep working at it and you can get it to .0002" or less.

[914Wilhelm]

Are you sure your tables even flat to .0008" in 12"? Put one hand on the miller head and push while you recheck your tram. I bet your machine is less rigid than you think. We push for these fantastic numbers but they are pretty hard to hit and while most of the time I am the limit to accuracy sometimes it is the inaccuracy and lack of rigidity built into the machine.

[darryl]

Just under a thou in 12 inches- that's not too bad. If you could find some half-thou shim stock, you might be able to get it better, but you should check this with the table in different spots also. You may find it pointless to try for any better than what you're already achieved.

[Jaakko Fagerlund]

One should also measure that the table top is flat to the dovetails and that the Z-axis dovetail is square to the table movement, otherwise tramming to 0.000000...1 is quite pointless.

[lakeside53]

The real test is of course milling something, then measuring it.

I once obsessed about always having the perfect tram... and apart from the other influences on final part gemoetry, most times I found I didn't need it. Often, the quckest way is to use soft jaws in the vice. One quick cut and you're done.

[mochinist]

The real test is of course milling something, then measuring it.

I once obsessed about always having the perfect tram... and apart from the other influences on final part gemoetry, most times I found I didn't need it. Often, the quckest way is to use soft jaws in the vice. One quick cut and you're done.

Youre talking about squaring up the vice jaws. If you cut vice jaws with an out of tram mill you can get bad parts(assuming some sort of tight tolerance of course)

[Tony Pratt]

.0008" in 12" is way way good enough! Just remember that if you are using a 3" cutter the out of tram on that will be .0002"
Tony

[Gunney]

Thanks for all the responses. I'm going to leave it be for a while, at least for a couple of projects, then check it again. Since the machine is brand new, I won't be surprised if it hasn't changed a bit. At that time, I may try to get it a little better. My goal in most everything I do is to do the very best I can, without going overboard. I guess I'm just figuring out where that "overboard" point is with respect to lathe and mill work. I like the idea of using a brake rotor, and based on that idea, I may even make a 12" diameter "tramming plate" on the lathe.

Patrick