Caveman Tramming Bar for Mill

I made it at TechShop!

This is just a quick and dirty project I made to add to my toolbox. When working with milling machines that have heads that can nod and tilt, it's important to check that the head is square to the table every once in a while. They can move occasionally due to vibration and you don't know who used it before you! This should be done especially before important cuts.

At TechShop they supply a super nifty tramming ring. It's a ring with three legs that sits on the mill table right over the vise with precision ground surfaces on the top and the bottoms of the feet. This way you just place the ring on the table, making sure there are no chips caught underneath, and sweep the top of the ring with an indicator. If the arm holding the indicator is steady, any out of square condition will show up as a difference in the reading on either side of the ring (x and y axis).

TechShop also has 2 good indicator holders for this purpose in the cabinet, but they're both "fancy" and I figured I'd show you guys how to make a simple one. That way anyone out there with a mill but not the fancy stuff will have something easy to make that works fine indicating off the table.

I called this the "Caveman" bar because this Instructable involves me beating the snot out of a steel bar. :D

I started with a piece of 5/8 1018 bar cut to an appropriate length. After measuring the the ring and adding a little for the curve and "stem", I added a little more so I could trim it to length after bending.

The stem of the indicator I want to hold is 3/8" diameter (basically standard). This should leave me 1/8" per side when I drill the hole through the bar for the indicator. Enough to flex a little, but not so thin it causes problems when machining.

Just clamp the bar in a stout vice, that is well mounted (bolted!) to a stout table. Make sure you clamp it with enough hanging below the jaws so you don't get teeth marks in the region you will be putting in a collet.

I did this cold, because I didn't have a torch, but if your not a big guy or girl, you'll want one. Just heat the region above the vise jaws to create a soft spot, letting the bar bend easier.

You could also just leave the bar long, giving you a great lever to work with, but since I wasn't using a torch I figured I'd be going to the hammer anyway. If you have a torch, leave the bar long and do it the easy way with a hot bend. ;)

Using a 2.5lb hammer from the wall, I unceremoniously beat the tar out of the bar. 5lbs would have been better, but the lighter weight really just meant "need more velocity". I had to straighten it up and re tighten the vise periodically, but overall it only took about 5 minutes with little rest breaks. Results pictured above.

This sort of project is excellent at telling you whether or not you should get back in the gym.

I definitely need to get back in the gym.

First pic shows how I added a neck to get rid of jaw marks and create a clear "clamp here" region on the stem.

Second pic shows the tool does indeed still have enough radius to get the job done.

I'm not sure why I chose the angle, in hindsight a regular 90* would have been better, but ah well.

I don't use drill presses much, so I used one here for a little practice. Don't ever try this one without a mounted vise and a drill press or a mill.

After a quick remeasure of the ring and a hairy eyeball for the indicator, I marked the appropriate spot on the bar, mounted it in the vise, and center drilled.

Making this hole straight and centered required a bit of help with a file. After center drilling, if the twist drill wants to walk off the center, stop and carefully start filing away the "high side" (rinse and repeat) until the drill gets started right.

A quick trim and bevel shown in the second pic and on to the fun stuff!

After doing this with the jobber length bit and the slightly sloppy drill press spindle, I have decided I still like screw machine drills and Bridgeports better. :D

For this next bit, I'll be using 5C collet blocks. For those of you not familiar, these things are super handy.

First pic shows the blocks (one square, one hex) on the right, and the collet closing lever (thingy) and nuts on the left. You use a nut to close the collet if you need the space, and the lever closer if you are going to be opening and closing it a whole bunch.

The second pic shows a 5C collet. These come in a bunch of different sizes and can even hold non-round shapes if you have the right collet for it. Like R8 collets, these only have a small closing range and don't like things that don't fit perfectly. Don't ever attempt to use these to hold things that don't fit VERY closely in the collet. You could easily bend the fingers inward or dent a face. Both of those mean the collet is now junk. Avoid.

My bar measured out fine on size and roundness, except for the hammer marks. Oops. 10 extra minutes with a fine file, sand paper, and calipers had it back to a collet friendly shape. Except for a few valleys, but they weren't big enough to cause an issue.

This is why collet blocks are handy. You can pop the square one right in the vice and easily cut features that are 90/180 degrees apart. The hex block does 60/120/180 degrees. Two, three, four, and six side objects are simple and quick.

Here I eyeball offset the vise, milled a screw flat, flipped the block, offset the vise the other way, milled a flat, and drilled a hole. Good times.

Be kind to whoever uses the mill after you and use an indicator in the spindle to re-square the vise.

Then, without loosening the block, I took it over to the vertical bandsaw and cut a slot. If you don't have a vertical bandsaw, careful hacksawing works fine, and reminds you about the gym again. :D

Don't put bench vise jaw marks in the collet blocks, though. That's just silly.

A little cleanup on the clamping surfaces was in order for proper function. A strip of sandpaper, shoeshine style, dressed up the stem nice, and wrapping a shorter bit around a dowel cleaned out the indicator mount hole nicely.

A couple of threaded bits from the hardware store and she works!

With the mill in neutral and the bar mounted in a finger tight 5/8s R8 collet, the indicator swings freely in a rock steady manner all the way around the ring. Not bad for 5 bucks worth. Remember, for this kind of operation the most important part is to closely couple the indicator body to the spindle axis. Everything else is just showing off. ;)

Also remember to not touch the ground surfaces of the tramming ring, they are unfinished cast iron and finger prints make them rusty.

The mill was to totally out of tram, BTW.