Tramming a mill

really precise enough to tram a head to the kind of accuracy I like.. Way to test: try some flycutting with a big dia cutter and you'll see what I mean..

steamer fired this volley in news:4ecff88a$0$1666 $ snipped-for-privacy@news.sonic.net:

Yep, but production vs. time dictates that you use the _minimum_ precision acceptable to the job. Since I'm now doing this for a living, I live and die by the "what meets the specs" requirement.

LLoyd

sits on top of them and may give a bad reading.

What I do is mill the top of a piece of stock with a relatively small (3/8") end mill. I then indicate a ring of this with a dial test indicator mounted to the spindle. This compares the spindle with the XY "plane" of travel of the mill, not the top of the table. The plane of XY travel is what is REALLY important, and you can't be sure the table is parallel to that.

My ancient Bridgeport has wear on the ways, and so it does not travel in a perfectly straight line, there is a slight arc to the travel. It also has enough dings on the table that it is iffy to indicate off that.

Jon

Kinda like that. I use a small sheet of glass instead of a brake rotor though. The indicator feeler doesn't chatter on dry glass like it does on dry metal.

(to use the coax indicator on real-actual-parts, I tend to squirt a track of oil for the feeler to slide around in)

Would that be regular window glass?

I have a old glass table top about 1/2" thick 24" square that i might try.

Best Regards Tom.

Yep. Mine's not that big though, it came out of a flatbed scanner that didn't have Win7 drivers available.

Aquarium (tempered) glass is a little more breakage-resistant, if you happen to ever get your mitts on a broken aquarium.

...Also to be honest, I have no idea what the typical +/- is of the surface of ordinary window glass. I'm just assuming it's much less than .001", since that's all I bother with worrying about anyway.

One can see and feel .001" variances on pieces of milled metal and nothing on window glass looks or feels even close to that big.

I am gonna give it a try, .001" is plenty good for government work. If i move the table X and Y with a indicator chucked in the spindle it should tell me how flat the glass is and if it can be used for tramming.

Best Regards Tom.

Well, the tolerances on size are pretty wild, but with how glass is made, I would have to say on a single sheet that the thickness/flatness would be pretty good..