HF Mini Mill Bed Tolerance

[Ray C]

If you can get it to a thou, I'd consider it good enough. After that, you're just chasing zeros on a machine that won't be able to hold that adjustment/accuracy anyway. Not saying you can't hold good tolerances on parts, because you can. And that's speaking from experience. But on these little mills things start flexing and moving quite a bit when under load.

Example: when you are tramming in Z, just reach up and push or pull gently on the head/column. Your indicator will move a few thou. The columns on these things (I have a LMS fixed column mill) are just not that robust. If you do like some people and you use a 1/2" or larger endmill, things will definitely flex more than a thou.

Just my $0.02,
Bill

I'm with Bill on this one. Thou, half-thou... -call it a day. I've only trammed my mills twice (after moving them) and I sweep-out a 4-5" circle and tweak things till it's as close to half-thou as possible. Then I'm good for another couple years. Assuming things are linear (which they probably aren't) this means you only have 0.00025 error/inch of inherent inaccuracy. -Not something you need to worry about in any kind of normal situation.

Without too much struggle, you can keep all your dimensions on smaller parts within a thou and if you pay more attention, even a half-thou. In all my general shop work, most parts much bigger than say 5-6 inches do not have tight tolerance requirements. Anything that has truly tight tolerance requirements should be milled slightly oversize and finished with some kind of appropriate grinding process.

On the rare situations that you need sub-half-thou accuracy in your machining processes, if you need it on a regular and predictable basis, you're playing in the wrong ballpark and should be looking at equipment with base prices close to the value of your home.

Ray

 

[Andre]

I've only trammed my mills twice (after moving them) and I sweep-out a 4-5" circle and tweak things till it's as close to half-thou as possible. Then I'm good for another couple years.
Ray

Really not trying to argue with you, but you really should tram it every few months at minimum. Especially is you have a mini mill, I have a BP M head and am surprised at how tram changes over a month.

Just my $0.02

 

[Ray C]

Really not trying to argue with you, but you really should tram it every few months at minimum. Especially is you have a mini mill, I have a BP M head and am surprised at how tram changes over a month.

Just my $0.02

Oh, I check them once in a while. Usually every month or so. They don't change any amount that I'm concerned about.


Ray

 

[nickmckinney]

Example: when you are tramming in Z, just reach up and push or pull gently on the head/column. Your indicator will move a few thou. The columns on these things (I have a LMS fixed column mill) are just not that robust. If you do like some people and you use a 1/2" or larger endmill, things will definitely flex more than a thou.

I bought one of these about 15 years ago, used it for a few months, then basically gave it to my friend as I gave up trying to do much of anything with it. He still cracks on how much it moves around but since he is one of the cheapest people I know he is still using it. Its so bad he gets on my baby 8x30 and thinks its a Rolls Royce while I am figuring which 10x54 is going to be adopted into the family as I like my machines kinda plump now.

- - - Updated - - -

Really not trying to argue with you, but you really should tram it every few months at minimum. Especially is you have a mini mill, I have a BP M head and am surprised at how tram changes over a month.

Especially with season changes. Concrete and steel both like to move around with temp.

 

[Beethovin]

I had tried shim stock under the base of the column mounting bracket to correct tilt on my Grizzly. Wasn't impressed with the results so drilled and tapped the bottom angle of the mounting bracket for Jack Screws (4). Now I can correct the tram as necessary. Wish I could say it makes resetting the column easier but it still takes time and patience to get it right.

Yes these little machines move under load, the head itself moves on the slide way and the column is twitchy when trying to make a heavy cut. Just part of what these little machines are, light duty and not very accurate. Even so its fun building precision? models with them.)

 

[tmarks11]

...I have a BP M head and am surprised at how tram changes over a month.

Over a month? How about over a day. A bit of a temperature change in your shop or a heavy cut with a face mill, and your out. We were taught at my school to check at the beginning of every shift, adjust it to within 0.002". Anything more than that on a BP was pointless, as the table, knee, etc, will give you that much movement during normal operations.

 

[6530]

Wasn't impressed with the results so drilled and tapped the bottom angle of the mounting bracket for Jack Screws (4). Now I can correct the tram as necessary.

Do you happen to have photos of this? It sounds like a great idea.