Uneven milling?

[redvan22]

Hi,
I have both a mini-lathe and mini-mill and I am following the instructions in an article about making tapered saddle gibs for the lathe carriage that are adjusted from the ends rather than underneath.

The first step is to make a tapered jig out of a piece of aluminum bar stock by placing a round pin under one end and milling until I have milled a taper.

Now, this is my issue:
I used a piece of 1" x 2" x 6" extruded aluminum bar stock to make the jig which I clamped down to the mill bed making sure it was flat and not lifted due to the way it was clamped.
After several passes starting from the high end to the low, I noticed that the machined edge on the low side was not perpendicular to the front edge of the piece. It was slightly angled to the left about 3-4 degrees.
After completing the taper operation, I measured the front and rear of the taper, on the high end and there was a difference of 12 thousands. This explains the machining edge.

Now, What does this mean?
Is my mill head not aligned properly to the bed or...?

I do not have a clue but it seems to me that I should not continue until I determine what is going on here.

Regards,
Red

 

[SamI]

It sounds to me like your head needs tramming (aligning) to the table. Having never done it myself I can confidently say that it looks to be quite easy to do! There’s a few good videos on YouTube on the subject. Could be worth a watch.

 

[markba633csi]

Long thin pieces tend to stress relieve and "spring" when machined, brass does it even worse. This may be what you are seeing
Mark

 

[richl]

You also need to make sure you are not bending the piece flat when you are clamping it down. It will spring back to it's natural shape when you unclamp it.

 

[redvan22]

It's it even possible to tram a mini mill head?

 

[richl]

I can send you links for your specific machine if you tell me what it is. Or do a Google search for tramming the head for your machine. From what I have seen and heard it's a matter of shimming, to get it trammed.
Welcome to the world of machining

 

[royesses]

Which mini mill do you have? Is it the fixed head or rotatable head? The rotatable head just needs you to loosen the fixing bolt/nut and rotate the head until it trams out. For and aft would need to be done with shims under the bottom bracket. The fixed head model would need shims under the column mounting bolts.

I have the HF mini mill with the rotating head and the tram fore and aft was .001" so no shims needed. The side to side was out by .003 and I adjusted it to .001".

I made the tapered gib mod on my mini lathe. I used a 1° angle block to make the aluminum jig for the gib. I made the gibs 2 inches longer than needed and drilled them for screws to hold the brass stock flat for milling. I tapped the holes in the aluminum jig to match the gibs. I used parallels to get the jig up high enough in the vise. I cut one side of the gib flat first and then mounted it and cut the taper. The brass will most likely warp and you will need to bend it flat again.

The tapered gibs work great. The most difficult part is making the adjusting screws and fitting them to the brass gibs. I made a slot in the gibs and made the flange on the screws wider than the slot. Then I filed the slot until the screw flange was a tight fit. There is no backlash between the screw flange and gib slot.

Roy

 

[redvan22]

Richi,
I have the micro-lux mini mill bought from Micro-Mark.

Mike.

 

[ThinWoodsman]

That one has a tilting column so you'll definitely need to tram it along the X axis by adjusting the tilt. It looks like the Y axis can be trammed by shimming the head.

 

[homebrewed]

I've found that extruded aluminum can have some twist. It often isn't all that flat on the other (wide) axis, either. For those reasons I usually start with over-sized stock and mill both sides, trying to remove about equal amounts so "skin" stress is -- hopefully -- balanced out. So what you're observing may just be the material you're machining.

The tapered gib mod for the mini lathe is a cool thing to make, but not necessarily better than a simple pair of slide plates, adjusted for a nice running fit using shims. Folks who have taken that approach report good results. Full disclosure: I'm among that group. Using something like molybdenum disulfide filled nylon, you aren't going to get much, if any, wear. I got it at McMaster.

Going back to the tapered gibs, if you go that route you will likely get some bow in the gibs once they are machined, so they will need to be bent flat. Hot rolled steel should have less internal stress so that's what I would use if I were to make the tapered gib mod.