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Toolmaker's Clamp

20 Jun 2019
Progress: Complete

At last I have access to a milling machine! And a traditional first project on a mill is a toolmaker's clamp.

The Bridgeport in question is at the London Hackspace which has recently moved to west London. For me at least that makes it a lot more convenient to get to. They need more members, so if you're reading this and you live vaguely nearby, make sure to sign up.

(Apologies if the pictures are not up to my usual standard, I didn't have my proper camera with me.)


My first cuts were very uneven, the shell mill was only cutting on one side because the head was out of tram. A digital angle gauge on the quill showed it was off by about 0.3 degrees compared to the bed. We could just straighten it up with the angle gauge but I thought I'd have a go at doing it properly.

First we remove the vice by undoing the bolts and sliding out the T-nuts. The vice weighs about 30kg so we really don't want to drop it on our toes.

Next we wipe down the bed and mount a dial indicator onto the spindle. One way of doing this would be to stick a magbase onto a drill chuck, but in this case I was able to borrow an indicator mount with a clamp designed for this.

Dial test indicator mounted to the quill examining the tram of the milling head

By carefully swivelling the indicator around we can accurately measure the angle between the head and the bed. There is a lot of wear in the bed, so it's important to make lots of measurements, moving around the bed to average things out.

To tram the mill left/right (which is where the problem was) we loosen the four bolts on the front, and then turn the bolt at the back right. As we approach the correct position, we snug the bolts down and move the last fraction by gently tapping the top of the head with our hand. We then tighten it properly and check it hasn't moved. In this case I was able to tram the head to within three divisions on the indicator (0.03mm, about 1 thou) which is plenty good enough, and certainly a lot better than it was.

I also measured the front/back (nod) and found it was within 4 divisions, which is good enough for me not to be bothered about it.

The last step is to mount the vice again, and make sure it is aligned with the Y axis. We do this by lightly tightening the bolts, tightening the jaws, setting the indicator on the fixed jaw and running the bed back and forth to see the alignment. Then tap it true with a soft hammer and tighten it down fully.

A dial test indicator mounted to the quill, used to tram the vice

Squaring stock

I started with a 12mm mild steel bar which was square enough to be held directly in the vice. The jaws have a lip which is easier to use than fiddling with very thin parallels. I took a few cuts and was happy to find that the shell mill was performing much better now.

Milling the top of the stock

With a reference surface established we rotate the part 90 degrees and clamp again, trying it both ways until the machined surface sits flat against the fixed jaw. Then we take another cut, and work our way around until all four sides are machined.

The dimension we're aiming for is 8mm so I tried taking a heavier cut and playing around with the feeds and speeds. Here is a nice shot of some coolant evaporating:

Large milling cutter plowing through material with coolant evaporating

The finish is OK, very good in places but ruined by the occasional scratch marks. I think this is due to wear or slop in the ways. Dismantling the bed and re-scraping the ways is an extremely labour-intensive project we can save for another day.

Examining the toolmarks

We've still got a fair bit of material to remove so I tried a few more permutations. This time doing a climb cut:

Large milling cutter plowing through material

This isn't really the right tool for getting a nice finish, but even so the results are somewhat underwhelming.

Steel section in the vice, showing toolmarks

Nose Angle

With the part to size we cut it in half with a hacksaw, and take off the burs with a file.

Two metal cuboids produced

Next I used our reference clamp to hold the two pieces together. By placing the saw marks together we know the dimensions of the two halves match exactly. My calliper measurement of 8mm was not particularly precise, so there is also a rotation to worry about. In this case the toolmarks are very useful for finding the orientation where the clamp holds both pieces evenly.

Two steel parts held together with a toolmaker's clamp

I used the nose angle of the existing clamp as a reference. The remaining bit of steel stock, with the machined side facing down, is used to square up the clamp's angle with the vice jaws.

Duplicating the angle from an existing clamp

It's not exactly precision work since the angle is basically cosmetic, but the technique seemed to work well.

Milling the large chamfer

I deliberately took this a little lower than we need, so that I could flip the parts and tidy up the blunt nose.

Milling the end of the parts

Lastly we want to tidy up the saw marks, which means transferring the parts to another clamp, without losing the alignment. Luckily there is no shortage of clamps around here.

Transfering the clamp parts, from one clamp, to another much bigger clamp

The reference clamp actually has rounded ends, but I think I'll keep the nicely squared ends on my version.

Two steel parts held together with a clamp and then held in the milling vice


I placed the first part in the vice and aligned the end of it to the end of the jaw. This will be our reference for when we swap the other part in.

The first hole was simply aligned by eye. It doesn't really matter if it's slightly off centre, so if it looks centred, that's good enough for me. From there I zeroed the DRO, so that the second hole is a known distance away.

Drilling holes in the part in the milling vice

The proper tap drill for M4 is 3.3mm. I have a few drills of that size at home but I forgot to bring them with me. 3.5mm is close enough, and it's probably a good thing to make the threads a little looser in a clamp like this. I felt confident enough to tap the holes under power, at very slow speed of course.

Thread tap held in the keyless chuck on the mill, ready to tap a hole in the part in the vice

The other part needs a clearance hole, a blind hole, and a further tapped hole to hold a bolt that keeps a little retaining piece in place. The reference clamp has a blind tapped hole for this bolt, I only had taper taps with me so I made it a through hole and tapped it M3.

The jaws fully shaped with a bolt in one of the threaded holes

Lathe work

It would have been nice to start with something wider, but I only had a 6mm steel rod to make these parts. In order to hold this small diameter I used a six-sided collet holder, held in the three jaw chuck. This is easily good enough for what we're doing, repeatability is of no concern here.

Round part mounted in the collet held in the three jaw

You can see a test knurl I'd done on the end there – that was not done with that much sticking out. The first step is to face and spot drill the rod for a live centre.

Steel held in a collet, facing the end and drilling a small divot for the tailstock

Using a clamp-type knurling tool is effective but I found it quite hard to get the knurl to track correctly. The problem is that the diameter is not matched to the tooth-spacing of the knurling wheels, but I don't want to take any more material off as these handles will already be a bit on the small side.

Closeup of the knurling tool in action

My solution is to have several attempts at it on the waste part of the rod, and once the knurl is tracking correctly we can walk it over to the other end.

Nicely knurled steel section

Beautiful. The rest gets turned down to 4mm ready for the M4 die.

Turning down a long thin part supported by the tailstock

There may be a tailstock die holder somewhere but for this I just used the drill chuck to keep it perpendicular while I turn the part by hand.

Threading the part using a die holder held with the tailstock chuck

I then switched back to the live centre for parting off. I parted off part of the way, then added a chamfer, then parted off the rest of the way. It leaves a little nub which can be removed with a file.

Closeup of the knurled part

The other part is pretty much the same thing except we add a little groove for the retaining clip. This was the narrowest parting tool I could find.

Cutting a groove with a thin parting tool

And with that, we are now able to clamp things!

Testing the clamp, by clamping something

Sheet Metal

This last little component is quite fiddly and tedious to make. Starting from a rather rusty bit of 1mm sheet, I used the sharp square edge of the remaining bit of square bar stock as a guide to try and form a joggle.

Side view of the sheet metal with a joggle in it

This kind of thing takes a lot of practice to get right.

Sheet metal with bend

Drilling holes in tiny pieces of sheet metal is a nightmare. The best thing to do is to hold it with mole grips or strong pliers so it's a little less likely to snag. My holes did not come out particularly clean, but given the shape we're working towards some filework is needed regardless.

The small shaped section of sheet steel

We have a working clamp! Truly, a thing of beauty.

The assembled clamp


The real joy of building a clamp like this, is that we get to spend the next few hours tediously lapping the surfaces to remove the toolmarks.

Part of the clamp, on some sandpaper

Starting with 120 grit, we work our way through the grades, with finer and finer grit, all the way to 2000...

Part of the clamp on some fine grade abrasive paper

Of course I only stopped at this point because I didn't have any finer polish. 2000 grit is almost but not quite a mirror finish.

Closeup of the very shiny surface on the steel jaws

The benefit of such a surface finish is that it's almost impossible to use the tool without covering it in fingerprints.

View of the finished clamp with mirrored surfaces

Another benefit is that it's very good at drawing attention to the corner that got damaged in the vice, which previously was well camouflaged.

The finished clamp, closed, with mirror finish on the jaws

Final touches

I realized after polishing it that I'd forgotten to drill cross holes in the handles. I didn't take pictures of this bit, but I put it back in the vice wrapped in thin cardboard so as not to mar the surface. It's difficult to drill into a knurled surface, sort of the opposite of having a centre-punch to line it up. I ended up filing a flat spot so it was less likely to wander.

The finished clamp

More ideas of things to do / ways to ruin it: