Mini surface gauge from "Lathework: a complete course"

Has anyone successfully made the "mini surface gauge" from chapter 2 of "Lathework: a complete course"? Did it work?

Here's mine:

I have made it but the fine adjust knob is unusably difficult to turn because I didn't manage to get the threads on the adjuster stud sufficiently precise.

Here's my adjuster stud:

You might be able to see that the M4 (smaller, longer) portion is "wavy". I attribute this to making the thread with a die in the vice, instead of using the lathe. The book suggests that a tailstock die holder would work better, but since tailstock die holders aren't introduced until chapter 7, we are told to cut the thread with a die for now.

Is there a trick to cutting straight threads by hand? Or is it a case that the part simply can't be reliably made to work until you can cut the thread in the lathe?

Welcome aboard, James

First let me congratulate you for attempting that job by hand … you will have learned a lot in the process.

I would think the best immediate/temporary fix is to substitute a good commercial cap-head scres.

To answer your specific question …

When doing such things ‘freehand’ : Instead of the standard approach, I often find it better to wind the nascent screw into the die … there seems to be a better balance of forces that way.

Alternatively you can use the [unpowered] drilling machine.

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Expect a flood of replies to your excellent opening question.

MichaelG.

If you don't have a die holder there is a trick you could try - Do you have a tailstock chuck? or something with a flat end that will fit in the tailstock? Put the die in the holder in the usual way and use the tailstock "implement" to push the die along straight and square as you cut the thread.

You may need three (or more!) hands the first time you try this but it can be done - just take it slowly and you will get a much better thread. Before you start to cut the thread put a good chamfer on the end of the blank part first to give the die a chance of starting square.

Another little "help" may be to make the blank a little overlong and then turn just the end down to the core diameter of the thread you are cutting so the die is held square before it starts to cut. Machine the extended end off after the thread is cut.

Hope that helps.

I made this device a few years ago as my first project. Mine didn't work either. The adjusting screw is very difficult to turn and has a very small adjustment range. I was unable to determine why it didn't work very well despite all its components being correctly and accurately made as far as I could tell. I put it on a shelf and gave it up as a bad job and moved on to stationery engines which brought me more success.

Jim

It would be another engineering exercise to figure out an alternative method to achieve the goal. Such as using a bit of M4 studding.

When cutting a thread with a Die, if possible, set the Die using a commercial capscrew / bolt / setscrew as a gauge.

A very small adjustment of one of the screws on the Die holder can make a HUGE difference to the thread. Easy to go from oversize to undersize in one move!.

Howard

Thanks for the many suggestions! Jim I'm not sure if it's encouraging or discouraging that your device didn't work either .

Making the part by cutting an M6 thread onto the head of an M4 allen bolt is an interesting idea, I hadn't thought of that. An M4 bolt on its own wouldn't work, the way this part works is the difference between the pitch of the M4 and M6 thread is used to either jack open or close up the slotted part of the base, to tilt the column over.

It has occurred to me that in use, the portion of M4 thread nearest the shoulder (save for the last couple of mm, which are also unused) is actually in use - and due to the taper of the die, this is also the portion of thread that is least well-formed.

So if I simply reverse the die and cut it as far as I can go, that might salvage it without having to remake the part. You can see in my picture that the last few threads are chunkier than the rest.

Failing that I will have another go at this part, and try Bizibilder's suggestion of using the tailstock to push the die square.

Edited By James Stanley on 01/03/2023 18:09:45

Adding to Bizibilder's suggestion, which is one I use quite frequently, I use a tailstock drill-chuck but open the jaws enough to give a degree of centring action to the die-holder.

You may find it tough going trying to thread the head of an allen head cap screw with a die. They are made of tough stuff that does not machine well in many cases. Might be easier to try the suggested die in standard holder guided by the tailstock chuck on a bit of mild steel.

If it's got to be right then I put the job into the lathe and set the tap with the tailstock and do it by hand

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I hadn’t thought of that either

One of the many useful features of Allen screws is the hexagonal socket … into which one might secure an hexagonal plug [secured by anaerobic retainer] … et seq.

MichaelG.

With due credit to Harold Hall

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MichaelG.

I would think the difficulty if getting it to work that Jim mentions is that the thumb screw is quite small so hard to get much grip to bend the metal base, changing the design to some form of pivot (pin and holes) would make adjustment by the screw easier.

As others have said back up the diestock with something in the tailstock and a change to metric fine may hale things a little easiier to adjust the tool as well as making threading easier.

The concept of using a flexure is excellent … it’s the detailing that will cause difficulty.

MichaelG.

Using the tailstock to keep the normal hand die stock square is a technique I have always used. Make sure the die holder is accurately made and the die seats properly in the holder. The dimples in the side of the die (if present) should align with the pinch screws so there is no tendency for the die to be prevented from seating against the back face of the die holder.
Mike

Well I am happy to report that I have made the device function, to an extent.

I re-cut the threads on the stud as tight as I could get my dies to go, and I also drilled out some of the internal threads in the "bush" part so that it is not engaging on such a long length of the stud.

It's still quite tricky to turn, but it does work. In the image below you can just about see the range of adjustment I get from the fine-adjust knob, it's about 1mm (but obviously varies depending on how far the scriber sticks out), see the 2 horizontal scratch marks on the can:

Thanks everyone for the comments and advice! I will remember the trick of using the tailstock to push the die for next time I need to cut a straight thread.

Ideally, using a tap or a Die on the tailstock, it needs to be able to slide (A fine thread will strip rather than pullm a mTailstock alongb the bed.

Also, a sliding Tap or Die mHolder apart from putting minimal loadv on nthe freshly cut threaf, shouldallow the tool to float a little on the arbor, so that it self centres on the work, and avoids drunbken threads

Howard..