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MachinistBlog.com

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

Snub’s ball turning tool

I think this is a brilliant idea.  “Snub” made a ball turning tool and used a 4-jaw chuck as the base.  He says it works perfectly and leaves an almost perfect finish.  I don’t doubt him because of the weight and rigidity of the chuck and the large bearing he used as a pivot.  His design also looks like it is quick and easy to make.  Notice that he didn’t make a holder for the carbide insert.  Instead took an existing holder and drilled it so he could bolt it to a piece of steel.

Unfortunately, you can’t use Snub’s idea if you have a small lathe.  It would definitely be too tall for a 7x mini-lathe, and I don’t think it will work on my 8×12 even if I use a shorter 3-jaw chuck and somehow directly mount it on the ways.

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 which no longer seems to sell them.  You can buy a nearly identical one from LittleMachineShop.com for about $155.  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

How to Grind and Use the ‘Contrary Finishing Tool’

This excellent article was written by Bob Bickerton, a new contributor to Machinistblog.com. It was originally published to the files section of the Yahoo 7x12minilathe discussion group.

The slowest feed rate on the Mini-lathe is about .004 in/revolution. This is fine for many applications but when you want a nice, smooth turned finish the slowest rate isn’t slow enough. You can set the knife tool to ‘rub’ and that helps sometimes. And, there have been modifications published that allow the slow feed to be reduced, but all require building something for the lathe. Here’s another option that only requires one to grind a HSS tool blank to a different shape. It’s a “Contrary Ground Finishing Tool” described by Frank Burns on page 58 of the Jul-Aug. 1997 issue of Home Shop Machinist magazine. Here’s how I do it.

I turn the OD of the work piece with the usual ‘knife tool’ until it’s about 10 thousandths oversize. Then I mount my ‘finishing tool’ and adjust the cross feed to just skim the surface (about a thou or so). Note the cross slide in feed dial reading. Measure the OD and set the cross slide to remove about half of the still oversize work piece. Measure the OD again, and if everything went well you should have removed half the oversize. If so, set the cross slide to remove the remainder and, presto, you have a nicely turned finish on specification size. If the first pass removed a little more or a little less than half, make an appropriate adjustment before the final cut.

Here’s a picture of some EMT conduit mounted in the chuck of my Cummins 7x12. EMT is welded steel tube and difficult to finish, at least for me. The welded seam can be harder than the surrounding area making it difficult to get a good, smooth finish. The front has been machined with my usual knife tool. The finish doesn’t look to bad but it is rough to the touch.

Here’s that same piece after using the ‘Finishing Tool.’ Hard to tell from the picture but the finish is very smooth to the touch. Because the tool cuts on the front it doesn’t need to be exactly on center height. You can’t cut up to a shoulder because of the geometry.

How to Grind and Use the ‘Contrary Finishing Tool’

Because of the high level of interest in this subject, I decided to show how I grind the tool and then show it in use. Here’s how I do it. Continue reading How to Grind and Use the ‘Contrary Finishing Tool’

Random Quote

Your mind is like a parachute. It only works when it is open.

— Unknown