I'm having a heck of a time tramming my mill.  I have these dial indicators:



The indicator mechanism seems a bit sloppy, but I don't know if it should seem more tight.

Here's my mill:


When I get everything trammed, at least as far as I can tell, drilling holes are still not perpendicular to the work.  They are slightly angled as though the column is rotated clockwise about a degree.

Does anyone have experience with indicators and tramming who can tell me if there's something I can do to nail this down? I'm open to buying different indicators.

Here's my tramming setup:

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You have to be off some place if your holes are not perpendicular. You really need something like a Bridgeport. I've seen some go for as low as $1300. Are you going from one side to another with your indicator? A regular dial indicator maybe better than the one you're using. Those type of mills are not built that well. Probably built in China. I have a regular #100 drill press and works fine for what I do. The lathe I have is pretty bad. Built in China. I use it to turn some things that don't need to be very accurate such as making a round rod from a square rod. I use these for rods coming from balls that are secured in hips, etc. A dial indicator something like this:


I'm not a machinist by trade but I have taken classes in machining. 

Larry Arpin said:

You have to be off some place if your holes are not perpendicular. . 

True enough.  And I'm hoping people here could help me fix that.

Larry Arpin said:

You really need something like a Bridgeport.:

Buying a different mill is not an option.  I considered including that comment in the original post, but decided not to assuming it would be kind of obvious.  Bad decision. BUYING A DIFFERENT MILL IS NOT AN OPTION.

OK. Now that that's taken care of, we now return you to your regularly scheduled internetting.

Larry Arpin said:

I'm not a machinist by trade but I have taken classes in machining.

Well, you're one up on me. I have never been fortunate enough to acquire expert training in any of the things I do for effects work.

What makes that indicator more better than others? I'm not suggesting it isn't, just asking.


This is just the ticket... a friend of mine has one and it's fantastic... I'm buying one for myself ASAP...


I don't have the time, experience or patience to mess with standard tramming procedures... it's worth a hundred bucks to take the guesswork out of the process and get on with the job.  I've got one of those Little Machine Shop spindle grippers for tramming and the flex and general instability of the dial indicator mount drives me crazy...

Speaking of good ways of spending money... 

... throw away that drill chuck and buy a nice ER25 collet set and holder for your drills and mills. I "discovered" these suckers when researching CNC router systems.  They come in different sizes, but the best general size for us is ER25.  You'll want the R8 version of course, I've got the MT3 one for my older MicroMark mill.  Mine came from China/eBay, but MicroMark sells a set for about the same money.


Better than standard collets, flexible enough for odd sized drills as well...  The problem with the drill chucks is that they never are as accurate (greater run-out) as the collets you use for your mills.  This takes care of that in one easy fix, and gives you back more up/down travel.

These two items (Pro Tram and ER25 set) have made a great impact in my productivity...


Jim Arthurs

I've learned something new here today!  Good thing we have experts in so many areas here.

I thought tramming a mill was going to be much more difficult... 

Thanks for the tips!

Jim Arthurs said:

This is just the ticket... a friend of mine has one and it's fantastic... I'm buying one for myself ASAP...


That looks like a handy tool.  The distance between indicators looks to be about 5.5 inches according to a picture I saw online, which means it could probably straddle my 3" vise and use my 1-2-3 blocks as the calibration surface. But if not I can pop off the vise to use this, and I bought the Turlen indicator to make it faster to square the vise.

Jim also said:

... throw away that drill chuck and buy a nice ER25 collet set and holder for your drills and mills...  The problem with the drill chucks is that they never are as accurate (greater run-out) as the collets you use for your mills.

I know what you mean about chucks. The blue tape around the chuck is a note that the runout is +- 0.001". How awkward is the swapping cycle for centering bit/jobber bit? I'm guessing in most cases you'd need a different collet for the two.

I'm not 100% sure because I've never had to dial in the head of a mill before,I've seen it done on a Bridgeport,so from my memory it appears that you are doing it incorrectly.You need to insert the dial indicatior directly into the drill chuck,that's where you hold it.For the bridgeport,there is a tool(a large ring)like a parallel bar but its a "ring" that is ground within very tight tolerances,about .0001,possibly more?It fits around the mill vice,but you can remove the vice to give yourself room.Mill vices are easy to dial back in.You lower the dial onto the surface of the ring,put a good .200 load on it and zero the dial.Work on one axis at a time(either X or Y).Break the gib nuts but keep them "snug",move the dial indicator on/to the axis's,zero the dial,check both sides and see which side is off moving from one side to the other.Say one side is .080 from the zero.Tighten the according  nut .040.Bring it back,re-zero the dial,check again.If it is off more,say it is is off .020,tighten the nut another .010,bring the dial back,re-zero,check again until you have the axis dialed in as tight as you can and snug the nuts good without moving the dial.You basically don't want the needle to move at all.Repeat for the opposite axis.After you have dialed in both axis,with the same load on the dial,run the dial all the way around to check the axis: (-X,+X,-Y+Y).The needle on the dial should not move more than .0005,well within .001.That's the correct way I remember to dial the mill head into your table so you make stait holes and don't mill unwanted angles.

Nick... nice mill picture, looks like it has a giant fly-cutter on it!  The RPM's are rather slow though... :)

Dave, you are very "lucky" your run-out is that small!  Both my drill chucks are much worse, both the one that came with the mill, but more surprisingly the nicer one from Little Machine Shop that hand-tightens is just as bad.  Maybe it's an MT3 spindle issue on the older MicroMarks?  Don't know.

There are two versions of that Pro-Tram tool... one that is 5" tip to tip and the other is 3".  I've not made up my mind which to get.  My friend has a larger mill and of course went for the full size unit, but both will work for our needs.  I'd go for the larger except I'm also eyeing an ER11 system for a CNC router spindle, and they only can take up to 5/16" tool shaft (the full size Pro-Tram is 3/8" or 1/2" center shaft).

On the ER collet holders, yes you'd need two different collets... they are super easy to exchange  if need be to move between small job drill and fat center drill shanks, or to just swap in/out drill bits, and the collets compress to hold all the intermediate sizes between any two collet "steps" in size.  Very handy.  MUCH greater grabbing strength on your bits than standard drill chucks.  I've literally hand-tightened the ER chuck sleeve (not designed for hand tightening, BAD Jim!) and it's held a fair sized drill bit through thick aluminium.

I'll make a video some time this week showing the operation and advantages of these collets over the standard collet/drill chuck process...

Jim Arthurs


Jim Arthurs

Good info, Jim.  Thanks!

John, are you talking about using a coaxial indicator like in this video?


Here's a reference to something more like what I've been doing:


I'm suspicious that there's too much play in the arm setup I have as well as in the indicator itself.  But I'm not sure if that's the source, or if there are other possible sources, or how to identify possible "other sources".

One thing about this mill is that the spindle can't be trammed. It's locked into the head with no adjustment options. So I really hope that it's aligned with the Z axis! But I don't know enough about this to tell if my problem is could be influenced by a hypothetical alignment issue there.

My procedure for tramming was from this mini-mill guide by Little Machine Shop...


Page 14 shows the two pieces of kit I use, and the next page shows the method.  I know there's too much play going on in that contraption, so that's why I'm going onto that two dial system.

That giant ring that John mentions is the EZ-Tram system, designed for "sweeping" the indicator on a nice smooth circle around the workspace...



<rant> I wonder sometimes what drug addict thought the nut arrangement for the column was a good idea.  There's so much flex in that thing. I ended up having a brace made that adds triangulation to stiffen up the front-back flex. Until then I'd get .010" flex. I couldn't mill a ball socket worth poop - it chattered more than squirrels in mating season - and countersinking for cap head screws was workable but unpleasant. </rant>

Yes, you can use a coaxial indicator,but a regular .0001 indicator works too.It just doesn't spin around like in the video.You have to manually move it from one axis to another.Its a little slower and more time consuming,but works just as good/the same.I don't know much about "mini mills".All mills basically have the same parts/components,but the mini mills might differ a little due to their size.Like,there's no "knee" and it might not have the gib/locking nuts that allow yoiu to move the head of the mill on its X&Y axis to mill angles.Most shops don't do that anymore anyway because it is such a pain in the A^%$#@$% to dial the head back in.I learnd on a  full sized mill like a bridgeport,but on most mills that is how it is done.I have all the "steps" in my very old text book,but I was going off memory.

Oh!Dave,I was looking briefly at the way they show you to do it on that link you posted.Since I don't know much about mini mills,its hard for me to give you the right information,but I can see how that will work too if you are only dialing in the X axis.The only problem I can see is the rod the dial indicator is on,it looks like it will give you an inacurate reading.I'd try that,but not have the indicator extended out all the way like that.I'm not sure though,maybe there is a reason to have it fully extended like that?I guess you don't have a Y axis to worry about?

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