Face milling lines between passes

[allamateur]

Far from being a pro at machining but, was that a new end mill ? Also if you didn't get your part flat and tight in the vice may be an issue. I have done this myself so that's why I can bring this up. Good luck and you will get it figured out.

Thank you. The end mill is used but doesn't look terrible. And the part was as flat as I could make it with some hammer taps, but the front parallel was still loose. I understand this is normal for a first-facing during a squaring-up operation though.

It looks like you probably have a tram problem on the Y axis. I have a piece of precision ground flat stock I use to check/adjust the Y axis on my mini mill.

On these machines, there are two main areas that can affect tram. The most obvious is the connection between the column and base. However, the connection between the milling head and column also can be out of whack. To check that, you will need a length of precision ground rod, often called drill rod, and a DI (dial indicator) mounted on a magnetic base. I have a length of 1/2" drill rod I use for this. Linear bearing rod would work very nicely, too. Some folks have used polished rod scavenged from dead printers. The main requirement is a smooth surface so the DI readings don't bounce around much, and large enough in diameter to not be significantly deflected by the force of the DI touching it.

The mag base is mounted on the side of the column with the tip of the DI on the rod, then the head is run up and down to check the alignment. To account for variations in rod diameter it usually is rotated to find the max and min readings, then the average is taken. Look up "RDM" or Rollie's Dad's Method". Do this for both axes.

If your head is misaligned w/respect to the column, the mounting bolts are loosened. Then the head is either rotated (for X axis problems) or a shim is placed between the head and column for Y axis problems. It likely will be necessary to remove some paint so you can rotate the head.

When I checked the head/column alignment on my mill I found relatively little misalignment, but every machine is different. Also, FYI, tramming the column will NOT compensate for misalignment between the column and head. If that's where the bad tram is, the head position relative to the work will change as the head is moved up and down.

I will try to retram the head and also investigate using this RDM method. I have some drill rod but it's 1/4" diameter, 11.5" long.
I am hesitant to believe it is tram though, as the Z-axis was not touched during the operation, and if the head were tilted forward or backward, the machined surface should be perfectly finished but tilted. What I have is a machined surface which has 0.002" steps in it.
Maybe tilt could do this though, if there is roughly 0.002" between column and head at the top of the head, it can fall 0.002" when the endmill has run off the part. Odd that the steps keep decreasing by 0.002" though, I would expect falling and then rising by 0.002" if this were the case. Nevertheless I will give it a go and maybe learn something along the way.

 

[Splat]

Besides tramming, get an endmill holder and use it instead of a collet.

 

[hman]

I think you should seriously consider tramming the column and/or head in Y. The goal is to have the spindle perpendicular to the table -or in other words- have the motion of the table parallel to the face of the cutter. Consider a case where the column axis is leaning toward the operator. For any given machining pass, the edge closest to the operator will be lower than the distant edge. Now take another pass with the table moved away from the operator. The surface of the table will (should!) be parallel to the Y ways. As with the first pass, the far edge will be higher than the near edge. It will also be higher than the previous near edge, producing a small step.

PS - as mentioned by @homebrewed, there are two sets of mating faces at play - the base of the column vs the base of the mill, and the mating faces of the two halves of the head. The head assembly is a lot less likely to be off than is the column base. But it MAY be an easier place to add shims for Y tram.

Note that the bolts which hold the head halves together are accessible only when the head is removed from the column. So to adjust Y tram, you'll have to keep removing the head, adding or removing shims, reassembling and re-measuring. Complicated, but less so than repeatedly removing the column from the mill base. The mating surfaces of the head are a lot smoother than the column-to-base surfaces, less sensitive to bolt torque, and the length of the surfaces involved is longer, so you can more "finely" tune the adjustment with the same thickness shims.

This photo shows where the head is split (I used a screwdriver as a pointer).


Tram Y first, re-checking after each shim adjustment, until it's satisfactory

Once you have the Y tram adjusted, you can leave the head bolts "just snug" and get a final X tram. The following photo (from 2011, when I'd stiffened the column with "epoxy concrete") shows the setup I used to make fine adjustment easier. I had the column on the bench for this, but the method should work just as well with the column in place. First, note the small aluminum plate I screwed to both head halves. This kept the bottom edge from shifting sideways. The steel bar and screw C-clamped near the top edge allowed fine adjustment of the X tilt. Once the tram was satisfactory, I carefully removed the head from the column (remember the "just snugged" bolts) and gave them a good tightening. Finally, I reassembled everything and verified tram in both axes.

 

[john.oliver35]

allamateur, before you start loosening bolts on your column and diving down that rabbit hole it would be helpful to establish a baseline set of measurements. This will also confirm if the tram is really the problem. It won't be hard to do if you have a dial indicator and some kind of holder arm. Take a look at Mr. Pete's oldest video on tramming. I believe he only uses simple equipment here (which you will need anyway to adjust the tram).

 

[allamateur]

I think you should seriously consider tramming the column and/or head in Y. The goal is to have the spindle perpendicular to the table -or in other words- have the motion of the table parallel to the face of the cutter. Consider a case where the column axis is leaning toward the operator. For any given machining pass, the edge closest to the operator will be lower than the distant edge. Now take another pass with the table moved away from the operator. The surface of the table will (should!) be parallel to the Y ways. As with the first pass, the far edge will be higher than the near edge. It will also be higher than the previous near edge, producing a small step.

PS - as mentioned by @homebrewed, there are two sets of mating faces at play - the base of the column vs the base of the mill, and the mating faces of the two halves of the head. The head assembly is a lot less likely to be off than is the column base. But it MAY be an easier place to add shims for Y tram.

Note that the bolts which hold the head halves together are accessible only when the head is removed from the column. So to adjust Y tram, you'll have to keep removing the head, adding or removing shims, reassembling and re-measuring. Complicated, but less so than repeatedly removing the column from the mill base. The mating surfaces of the head are a lot smoother than the column-to-base surfaces, less sensitive to bolt torque, and the length of the surfaces involved is longer, so you can more "finely" tune the adjustment with the same thickness shims.

This photo shows where the head is split (I used a screwdriver as a pointer).
View attachment 370492

Tram Y first, re-checking after each shim adjustment, until it's satisfactory

Once you have the Y tram adjusted, you can leave the head bolts "just snug" and get a final X tram. The following photo (from 2011, when I'd stiffened the column with "epoxy concrete") shows the setup I used to make fine adjustment easier. I had the column on the bench for this, but the method should work just as well with the column in place. First, note the small aluminum plate I screwed to both head halves. This kept the bottom edge from shifting sideways. The steel bar and screw C-clamped near the top edge allowed fine adjustment of the X tilt. Once the tram was satisfactory, I carefully removed the head from the column (remember the "just snugged" bolts) and gave them a good tightening. Finally, I reassembled everything and verified tram in both axes.
View attachment 370493

I have to apologize, I had trammed the machine in to the best of my knowledge when I got it a month or two ago, and don't remember more than 0.001" in either X or Y using a little spindle DTI holder. I went and checked again (on the table itself, all I have for precision ground surfaces are parallels but there's nothing to hold them there and they're too thin not to fall over between measurements/when hit with the DTI) , here's what I found:

B&S 0.0001" DTI:
Y: 0.0030 - 0.0045" from front to back of table, a length of about 3.6875"
X: 0.0001" one time I did it and 0.0005" or so another time. length of probably 10-12".

Shars 0.0005" DTI:
Y: 0.0045" - 0.005" from front to back
X: 0.0000" - 0.0005".

These ranges are from doing the measurements several times. I don't think I trust my tenths DTI anymore. It's an old used Brown and Sharpe tenths DTI that I got for free. I compared it here with a new Chinese DTI I bought. So anyway I think I will be using this guide of yours and I appreciate the details. I might order some 1-2-3 blocks to double-check this since the table itself isn't perfect. I also would appreciate any advice about how to compare DTI's to know which is getting a more true reading (to within its own finest graduation at least) - are there 0.010" tall precision ground ramps or something which can measure this?

I also understand about the cuts now - I had erroneously assumed the head was moving along its relatively non-square Y-axis in relation to the part, but the part is moving along the table's square Y-axis to the head, creating these repeated slopes for each pass having the same average height between them, which form ridges at the edges.

allamateur, before you start loosening bolts on your column and diving down that rabbit hole it would be helpful to establish a baseline set of measurements. This will also confirm if the tram is really the problem. It won't be hard to do if you have a dial indicator and some kind of holder arm. Take a look at Mr. Pete's oldest video on tramming. I believe he only uses simple equipment here (which you will need anyway to adjust the tram).

Thank you John please see the measurements above. It took me some convincing to recheck the tram but you guys were on the money, unfortunately for me.

 

[hman]

It's all good ... and it's all learning. I'm still learning (from my mistakes) as I go. Keep us informed of progress.

 

[Illinoyance]

I use a 4" face mill in a Bridgeport. Even with the machine trammed perfectly I see a definite line between overlapping passes. The line is visible but cannot be felt with a fingernail.

 

[hman]

What I've heard from multiple sources is that you can "feel" height differences of about 0.001" with the tip of your finger. I'll bet the fingernail test is even better. So the line you're seeing but not feeling is probably on the order of 0.0001".

 

[Winegrower]

My experience is that it’s not possible to have adjacent milling machine passes that are not visually discernable,
i’d appreciate any proof to the contrary.

 

[allamateur]

I use a 4" face mill in a Bridgeport. Even with the machine trammed perfectly I see a definite line between overlapping passes. The line is visible but cannot be felt with a fingernail.

This is the goal. Currently the ridges between passes can probably be felt with an elbow. There is 0.002" between each pass.