Small knurled knob

[Tiger]

I'd like to make a small metal depth gauge. The locking mechanism will be a small threaded bit of steel with a small knurled head. How would you go about making this part? Would you put the knurl on first and then thread it or put the thread on first, then knurl. The piece will be no larger than 3/16 inch so I'm concerned about the small diameter and the possible flex that will occur when it's machined.

[bollie7]

Tiger
If I'm reading this right you want to make a small screw with a knurled head?
If so I'd knurl it first, then machine the end down for the thread. thread it, then part it off. To finish the end where you parted it off, take a hex nut that fits the thread, slit it by cutting with a hacksaw on one flat (cut along the axis of the thread) As this is quite a small thread you will have to clean the threads in the nut after you have cut it. If you have a tap the right size then that would be ideal. Put the split nut on the knurled screw and then hold the nut in the 3 jaw chuck so the split flat is not under a jaw. when you tighten the chuck the split nut will tighten on the screw. you will then be able to finish machine the head.
As the screw is only small, another way to machine the head would be to grind up a small form tool from HSS so you could finish the end of the head (I'm assuming you would want some sort of domed/curved end?) and part it off in one operation.

Hope this helps

bollie7

[Grahame Collins]

Having recently performed some knurling on a small diameter ,I can tell you that deflection from the side thrust of the knurl will present problems unless you follow a procedure.

There are probably other ways but this works for me.

My way of attacking it would be

Use a larger diameter -say 12mmdiam x 35mmL - to start with short stick out from chuck < 3 diameters.


face
center drill
drill tap diameter
tap
turn Od- leave relief after the shoulder area for the knurl to run over
knurl
part off


Grahame

[Tiger]

Thanks Bollie and Grahame. The split nut idea really helped me finish off the head of the screw. I did find the thin probe that measures the depth a problem though. It is approx 3 mm in diameter and about 70 mm long and the flex made it difficult to get an even diameter. How can you accurately machine thin material so that you can at least minimise flex if not remove it all together?

[Grahame Collins]

It is approx 3 mm in diameter and about 70 mm long and the flex made it difficult to get an even diameter. How can you accurately machine thin material so that you can at least minimise flex if not remove it all together?

I did'nt realise that the thread was external. I wrote the sequence with an internal thread through the knurled knob in mind.

Anyway on to the machining. Most lathes are supplied with a travelling steady and its this tool that supports the opposite side of the shaft where the lathe tool cuts.It resists the tendency of the shaft to deflect under cutting pressure of the tool.
You can ID the travelling steady as it will have two supports and open front while the fixed steady has 3 supports and a hinge over assembly.The contact surfaces of the arms are made of brass or some material softer than the steel it supports.
The travelling steady attaches to to saddle somewhere. On my lathe it is the front.

Grahame

[pipeclay]

Support the end of your job with a live or dead centre.

For a 3mm dia you might be pushing it to use a travelling steady or any steady that is not purpose made for such small diameters.

Not all steady fingers or supports are made of material softer than that being machined.

[Grahame Collins]

Thanks Pipeclay,

I stand corrected on those points.

The next question obviously is:

What is the factor that limits the minimum turning diameter using a steady ?

Grahame

[arose62]

I wanted to get a better grip on a small knob, but have neither knurler nor knowledge. (lots of "kn..." words there - I'm a knewbie at lathes :)

So, what I did was run the carriage back and forth to cut a groove down the side of the knob, turn the job a bit, repeat, etc.
I used the teeth in one of the gears to index my way around, so the grooves were evenly spaced.

Effectively gave the same appearance as using a straight knurl.

Cheers,
Andrew

[pipeclay]

Hello Grahame,having never tried turning anything that small with a steady I can only give my opinion,but the limiting factors for there use would be goverened by the physical dimensions of the fingers or supports.

Just like 3 Jaws chucks either Drill or Lathe,as they approach centre there jaws meet limiting there holding capacity.

I suppose for continued small diameter work (less than the working diameter of the steadies one could make there own fingers to support the diameters they work to,after all its the tips of the steady that will interfeer with the work holding.

[Big Shed]

Or one could drill an appropriate sized hole in a bit of round bar and hold that in the steady?

[Tiger]

I wanted to get a better grip on a small knob, but have neither knurler nor knowledge. (lots of "kn..." words there - I'm a knewbie at lathes :)

So, what I did was run the carriage back and forth to cut a groove down the side of the knob, turn the job a bit, repeat, etc.
I used the teeth in one of the gears to index my way around, so the grooves were evenly spaced.

Effectively gave the same appearance as using a straight knurl.

Cheers,
Andrew

Good idea, Andrew and all done without turning on the lathe. How many passes did it take before the impression was satisfactory?