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Plans, projects and how-to's for home machinists

How I tram my mini-mill

This is how I tram my mini-mill.  I think the method I use is fairly common, although I may use slightly different equipment than others.  There are other ways of doing it and some people have strong opinions about which way is best.  I’ve included links at the bottom to some interesting discussions I found if you would like to learn more.  If you don’t know, tramming is the process of adjusting the mill’s column so the spindle is perpendicular to the table.

By the way, this procedure only trams the X-axis.  Unlike most other mills, the mini-mill’s Y-axis is not adjustable, although there are ways of doing it if you’re willing to go to the trouble.

My Equipment

  • A matched pair of 1-2-3 blocks
  • A digital dial indicator
  • The fine-adjustment arm from an inexpensive magnetic base for a dial indicator held in a 5/8-inch cross-drilled piece of drill rod mounted in a collet

I started using the arm from a magnetic base because it was the quickest and easiest way to mount a dial indicator so I could read it from the sides of the mill.  It replaced a home-made one that had the DI facing forward (good) and to rear (hard to read).

If your mill vise is big enough you can measure on the top of it with a dial test indicator (DTI) and tram your mill that way.  The vise shown in the picture is probably big enough to do that.  But the screwless precision vise I often use isn’t, which is why I use the 1-2-3 blocks, a trick I learned from someone else.  The blocks will also allow you to tram your mill without removing the vise.  I also believe you can get better results by taking your measurements farther apart.

For Best Results

Before you get started you should swing your indicator from one side to the other a few times to make certain you get repeatable measurements and there is no “play” in your setup.  You should also center your table under the spindle and make your measurements on its center line and at the same spots each time.

You should know that tramming your mill’s table does not guarantee your vise will hold your work pieces square with the spindle.  It should if it was made properly.  If it doesn’t you should find a way to fix it, consider getting another one or tram your vise instead of the table.  I’m talking about your vise being square with spindle, not with the table.  That’s also important, but it’s different topic.

One way to check your vise is to tram your table, mount a long parallel in it, and then measure at the ends of the parallel with your indicator.  It should be just as perpendicular to the spindle as your table, or pretty darn close.

It’s Easier with a Digital Dial Indicator

In the past I’ve always trammed my mill using a traditional dial indicator with a needle and dial.  Sometimes it would take me just 2 or 3 minutes but other times I’d be scratching my head for 10 or 15 minutes and wondering what the heck I was doing wrong.  It was usually because I’d gotten confused reading my “analog” indicator, which is easy is for me because as an amateur machinist I don’t use one very often.  So the last time that happened I took my old indicator off and replaced it with the new digital dial indicator I’d bought from Harbor Freight for about $25 (with a 20% off coupon).  It instantly put an end to my confusion.

The Procedure

The procedure is simple with a digital indicator.  Swing your indicator to one side and zero it.  Then swing it to the other side.  If the measurement is “negative” then push the column toward that side half the distance shown on the indicator.  If your measurement  is “positive” then push the column away from that side half the distance shown.  Then zero the indicator again and swing it to the other side to check your work.  You want to try to get the same distance on each side,  although I wouldn’t worry too much if you’re only off a thousandth or so over a good distance (my setup takes measurements about 10-inches apart).

If your indicator has a needle, then use it to find out which side has the shortest distance between the indicator and the table, and then “zero” it or write down the measurement.  Then swing it to the other side, calculate the difference in length and push the column toward that side half that distance.

Before you can adjust the column you’ll obviously have to loosen the big nut on the back of it a little.  There’s a good chance that the column will move slightly when you tighten it again, so re-check the tram.  I’ve found you can minimize that if you loosen the nut just enough to allow you to move the column by gently tapping it with a rubber mallet.

More information

CraftKB: How to tram a Sieg X2 mini mill

Practical Machinist Forum: How to tram a mill for best surface finish / flatness?

How-to: Remove the intermediate gear from a mini-mill

This photo essay will show you how to remove the intermediate gear and shift lever from the head of a Sieg Industries X2 mini-mill [HF 44991, Grizzly G8689, Micro-Mark & others].  It also explains why you might want to do so after installing a belt-drive.  You may also find it useful if you need to replace a broken intermediate gear.

Why you may want to remove the gear

I’ve installed a belt drive kit on two different mini-mills.  With the first one I didn’t feel there was any need to remove the intermediate gear.  But the second mill had a much noisier gear train, both before and after I installed a belt drive. It also had a very slight vibration when running the spindle at high speeds.  Removing the gear made it much quieter and eliminated the vibration.  By the way, belt tension can also cause your mill to be noisy.  I suggest you experiment with it if that’s your issue.

This might be a good time to check and fix your spindle/column alignment

Mini-mills sometimes suffer from a misalignment of the spindle and column that can’t be fixed by tramming the mill.  Fixing it requires removing the head from the column, which you’re going to have to do anyways to remove the intermediate gear.  So this would be a good time to check your mill and fix it if it’s misaligned.  Earl Hackett wrote a nice procedure that will tell you how to do it.

I chose not to because I didn’t have a lot of time and I plan to take my mill apart again for some other modifications.

I suggest taking the following precautions if you do this

  • Disconnect the power to your mill.  You don’t want to accidentally turn on the motor.  You’re also going to have to open up the control box to remove it from the head.
  • Be careful when disconnecting the torsion-arm spring that supports the weight of the head.  You don’t want your fingers to get pinched, the bolt to fly into your face, or the head to suddenly drop onto the table.
  • Don’t strain your back or hurt yourself in some other way while lifting the head off the column or reinstalling it.  It’s heavy and it may put you in an awkward position.  It would be good to have help.
  • It’s always a good idea to wear safety glasses in a workshop.

The first step is to remove the head from the column

You’re going to have to slide the head off the column before you can remove the intermediate gear.  I’m not going to describe in detail how to do it because I have a CNC mini-mill and the procedure is different for a manual mill.   But in a nutshell, you’re going to have to disconnect the support spring for the head (be careful that you don’t get hurt by the spring or let the head drop onto the table).  You’re also going to have to remove the control box mounted on the side of the head by removing three screws inside the box (Make certain you’ve unplugged the AC power cord first).  You’ll also have to remove the motor and spindle nut.  My article about installing a belt drive can show you how. Continue reading How-to: Remove the intermediate gear from a mini-mill

How-to: Install a belt-drive on a mini-mill

I wanted to move the belt drive from my old mill to my new CNC mini-mill.  Well, the spindle nut didn’t want to come off, which didn’t make sense because I didn’t have any problems putting it on six months earlier.  I went looking for pictures and advice on the Internet and had trouble finding any.  So I wrote this article.

My goal is to:

  • Show you how quick and easy it is to install a belt-drive kit on a mini-mill.
  • Discuss the advantages of using a belt drive.
  • Tell you about a dumb mistake I made so you won’t do it.
  • Briefly explain bearing preload and how it can cause your spindle bearings to get too warm after you’ve installed a belt drive or taken your head apart for some other reason.

The belt drive kit for my mini-mill was made by the Steele Company.  It cost about $130 and you can either buy one from them or LittleMachineShop.com.  It’s pretty easy to install and will probably take about 20-40 minutes.  You can also find plans and instructions on the net if you would like to build your own.  If you can make a pulley on a lathe then it shouldn’t be too hard.

There are some good reasons for installing a belt drive:

  • It will eliminate any chance of breaking a drive gear, which can happen pretty easily if your cutter jams.  Instead of a gear breaking the drive belt should slip instead.
  • It will increase the top speed of your spindle from about 2500 rpm to more than 4000 rpm, which is important if you use very small end mills or drills.
  • Your mill will run much quieter.
  • A belt drive may also make it easier if you ever want to mount a different motor on your mill.

Before you install your belt drive I suggest turning your spindle on as fast as it will go and walking away from it for about 10 or 15 minutes.  Then feel or measure how warm the milling head gets.  That’s about how warm it should get after installing the belt drive.

The bearings in my CNC mill’s head started running hot after I installed the belt drive because I tightened the spindle nut just a little too much.  The more you tighten that nut the more “preload” you give your spindle bearings.  You want to preload them enough to eliminate the internal play in them (which can cause run-out), but not so much that you cause excessive friction, heat and premature wear.  The nut doesn’t need to be tightened very much and I only had to loosen it a little to fix the problem.

One thing you’re going to have to do is to unscrew the spindle nut on top of the head.  There’s two things you need to know before you do that:

  • It has a left-handed thread, so it’s going to turn it the “wrong” way.
  • Before you start unscrewing it you need to loosen the set screw in it.  That was my dumb mistake.  Even though I’ve seen it many times I still forgot it was there because it was facing away from me when I inserted the pin to lock the spindle.  Luckily, I stopped turning the wrench before I did any real damage.

Disclaimer:  This is an overview.  These instructions are not meant to replace the ones that come with your belt drive kit. Continue reading How-to: Install a belt-drive on a mini-mill

X2 Mini-Mill Mod Reduces Column Flex

Mini-Mill Column Modification

There’s an excellent thread over on the Home Model Engine Machinist forum that describes a modification for reducing the X2 mini-mill’s notorious column flex.  It looks like it would be fairly simple to do.  The hardest part might be cutting a 1-inch thick steel plate to the proper size (or paying to have someone else do it).

You’ll also have to drill and tap holes in the mill, but the author demonstrates how he did it with a hand-held electric drill.

I’m wondering if this mod could significantly improve the mini-mill’s ability to remove metal by reducing chatter so you could make faster or deeper cuts.

Random Quote

It is our responsibilities, not ourselves, that we should take seriously.

— Peter Ustinov, Author & Actor