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MachinistBlog.com

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

Dial Indicator Helps Set Z-axis Height

I bought an old Federal dial indicator from a retired machinist that had a big flat donut-shaped magnet glued on its back.  I almost passed it up because it was kind of ugly, but it has turned out to be one of the most useful tools in my workshop.  It is particularly useful for adjusting the Z-axis height on my Harbor Freight mini-mill.

I’m a little mistrustful about dialing in the height because of the huge amount of backlash in the Z-axis.  So I often stick my DI on the column and use it to set the height or to double-check the dial and make certain I haven’t miscounted the number of turns I’ve made.  It only has a range of 1-inch but that’s all I need most of the time.

It was really helpful last night when I needed to remove a very small amount of metal using a fly cutter.  The indicator showed that the head was dropping another 3-thousandths when I tightened the gib lock (which is one way to protect yourself from the mini-mill’s infamous “head drop problem“).  I hadn’t experienced that problem before and I hope the gibs just need to be adjusted.

A couple of potential problems

To get the most accurate reading your indicator’s plunger needs to be perpendicular to the head.  Instead of eyeballing it I’ve thought about building a magnetic mount for one of my other indicators that would slide up and down against the column’s dovetail.  It would make it easier to position the indicator and ensure it’s always perpendicular.  I didn’t have a big enough block of aluminum the last time I was going to make one and this morning I was wondering if it would be easier, cheaper and faster to just buy another column stop and modify it to hold an indicator.

And lastly, a more experienced machinist once told me you can ruin a cheap poorly-made dial indicator by sticking a magnet on it. Continue reading Dial Indicator Helps Set Z-axis Height

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

Inexpensive DIY tachometer for a mill or lathe

It looks like Adam mounted the sensor in the spindle cap and is using putty to hold the magnet on the spindle. I would have done it a little differently.

Here’s an idea I haven’t seen before.  Adam made a very inexpensive tachometer for his variable speed X2 mini-mill using a cyclometer (bicycle speedometer).  Almost any wired cyclometer will work and you should be able find one with a nice big display for less than $15.  (You probably don’t want to get one that has a wireless sensor because they’re more expensive, you’ll have an extra battery to replace occasionally and you might get erroneous readings caused by the receiver picking up electrical noise from your motor).

Someone left a comment with a link to a tutorial on Instructables with more details about making one of these.  The author, Jose, explains that you basically just have to glue the magnet that comes with the cyclometer to your spindle and somehow mount the sensor within about a 1/4-inch of the magnet when it spins around.

The sensor sends a signal to the cyclometer every time the magnet goes by it.  The cyclometer uses that information to calculate the bike’s speed using the wheel’s circumference, which you have to tell it.  In this case though, we don’t want to know speed, but RPM instead.  Jose says to use 268 mm for the wheel circumference if the cyclometer displays the bike’s speed in MPH, and 167 mm if it displays in KPH.

He says those numbers will display the RPM in hundreds, regardless of circumference of the object you mounted the magnet on.  I don’t why that is, even though I was once good enough at math to get an A in college calculus III.  There’s a chance I’ll wake up in the middle of the night with the answer, or have a revelation while in the bathroom.  But just in case I don’t, I would appreciate it if you would leave a comment with the answer if you have a good “explanation for dummies.”

Random Quote

The difference between stupidity and genius is that genius has its limits.

— Albert Einstein