HF Mini Mill Bed Tolerance

[ronboley]

Sure this is a newbe question. I have a new HF Mini Mill that I'm setting up. Question is...I'm tramming the mill bed and can of course set the bed left to right to a very close tolerance, but...I assume the bed should be pretty close front to back as well??? Using the tram set up my bed reads .075 difference between the front and back of the bed. Is this a lot? Although the bed seems flat to me, this front to back difference in relation to the mill spindle seems a lot to me. Is there a way to "adjust" this? Or is this just like lady gaga says, its the way I'm made?

 

[Don B]

That is a lot...! .075 WOW, I would consider .005 a lot, I'm not familiar with HF machines but can you shim it..?
I'm sure someone will chime in that owns one, I'll be interested to see what they suggest, good luck.)

 

[wrmiller]

you will have to shim the column along the y-axis to get it perpendicular to the table

Bill

 

[n3480h]

My HF minimill also had the issue, but not that bad. First thing I did was to check if there was "foreign material" (pun intended) between the column and the flat where the column mounts. There was, and I cleaned both the flat and the column, but I still had to place .003" shims on my column to get it within .001 in Y axis. If the column leans forward, the shims go high, if it leans back, the shims go low. It gets a bit tricky, because backing out the single column mounting bolt enough to get a shim inserted will usually screw up X axis. I did the Y shim, then set X perpendicularity. Never got it perfect at the table's extremes, but pretty close. Plan on spending some time and don't get frustrated, you'll get it (at least a lot better than .075"). With that done, you get to check if your vise, rotary table, or other work holding fixture is parallel to the bed. Isn't this fun? :lmao:

Tom

 

[Ray C]

Woah, woah.... slow down. 75 thou is huge. With all due respect, are you sure you're measuring properly? How is your indicator setup to perform the measurement. If you're using a rotating type, is it rotating at 90 degrees perpendicular to the shaft? Man, 75 thou is way off...


Ray

 

[darkzero]

No way it could be that much off unless it was damaged or has a manufacturing defect.

Check the Y axis gib adjustment (won't hurt to check Z also), lock the qill, & lock the head (column), then measure again.

 

[Don B]

No way it could be that much off unless it was damaged or has a manufacturing defect.

This is so true, if this mill is new as in "brand new" I'd be marching it right back to the store for an exchange.:thinking:

I'm not sure how big this mill is but if the column can come off easily you could try a straight edge across the mating surfaces to see if theres anything raised that's not allowing it to seat properly, if you have an angle plate you could try that against the surfaces to see if sits flat or rocks.)

 

[ronboley]

Rest Easy...I slipped a decimal point...it's .0075 out front to back in it's 3-1/2" width....I suppose I need to run the bed thru it's front to back travel and get an overall number...still a lot and will shim the column to try to get it closer...what tolerance should I expect to achieve in the bed width of 3-1/2"??...thank you all for your great advice!

 

[Don B]

what tolerance should I expect to achieve in the bed width of 3-1/2"??...thank you all for your great advice!

I'll not qoute an exact reading but if it where me I'd be looking for tenths.)

 

[wrmiller]

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