Silly questions on thread chasing!

[tea lady]

I acquired a par of thread chasing chisels at the Melbourne Wood Work Show. I got the only matched set in the box of bits and pieces. They are 5 TPI witworth! Which I know is kinda big: shrug: having read the other threads recently about Cliff and TTIT's efforts. And Huigh's referances.

My silly question is.......
Do I have to have a specific diameter (or multiple there of ) for a particular thread size? I can imagine with such a big thread getting round to the start again anf the treads not meeting up! What would go with 5 TPI ?I guess it depends on the slant of the thread? :brainhurts:

Picks of said tools. Unhandled, blunt and dirty as yet!

[Allan at Wallan]

I reckon they are the onesI looked at last year
and finally decided not to buy them.

Hope you have success with them ... I was not
game to take a chance and find them unsuitable.

Allan

[powderpost]

Tea Lady, I think it may have been me that was playing with Cliff. You will have a lot of trouble with a thread that size, especially with little experience. There is too much wood to be removed to create a decent thread. Also the crest of the thread is quite brittle and will break of easily. Sharpen the chasers before you start by rubbing the top flat on an oil stone or the side of Robo's tormek, if permitted.

No you don't need to have a specific diameter to cut a thread. You just start chasing. You will need to make an external thread or internal, and then match the apposite to fit. Then measure the differences for future reference. However, metal thread tapping charts will help give you a guide as to the difference between the male and female sizes before cutting matching threads

I would suggest you find a bit of the hardest timber you can and play with the external chaser to start with.

If you want to chase threads, get a 1.5mm chaser from Hughie, I believe he is making some now. 20 tpi chasers are definitely the way to start.
Jim

[tea lady]

Tea Lady, I think it may have been me that was playing with Cliff. You will have a lot of trouble with a thread that size, especially with little experience. There is too much wood to be removed to create a decent thread. Also the crest of the thread is quite brittle and will break of easily. Sharpen the chasers before you start by rubbing the top flat on an oil stone or the side of Robo's tormek, if permitted.

No you don't need to have a specific diameter to cut a thread. You just start chasing. You will need to make an external thread or internal, and then match the apposite to fit. Then measure the differences for future reference. However, metal thread tapping charts will help give you a guide as to the difference between the male and female sizes before cutting matching threads

I would suggest you find a bit of the hardest timber you can and play with the external chaser to start with.

If you want to chase threads, get a 1.5mm chaser from Hughie, I believe he is making some now. 20 tpi chasers are definitely the way to start.
Jim

Sorry! Blond moment! Never good with names.

I knew they might be a it big! But they were the only matched set there!

Will have a fiddle with them next week. I'm sure will be curious to have a go! At least his lathe can be turned down in speed. Although I don't think they have ever gone that slow!

[powderpost]

Tea lady, you will need to come down to between 200 and 400 rpm. Would recommend about 200 to start with. And, I can't emphasise enough, a really really light touch.
Oh, and your question is not silly at all...
Jim

[tea lady]

I reckon they are the onesI looked at last year
and finally decided not to buy them.

Hope you have success with them ... I was not
game to take a chance and find them unsuitable.

Allan

Chicken!

Was even thinking I might be able to use them on my pottery if they are too big for wood!

[Cliff Rogers]

What Jim said.

[hughie]

Tea lady,

Thread chasing is not difficult when you understand some of the basics.But it will require practice,often lots.

You dont need a set or specific size, but do need to have a size difference ie that is the depth of your thread effects the male and female diameters. In this case your 5tpi thread depth is 3mm.

So what ever size the male part is. The female or internal thread will need to be 6mm smaller ie 3mm per side for 5tpi Whitworth.

Thread depth will vary as per each tpi or pitch, below is a chart that should shed some light on the matter....hopefully


Thread Data Charts

So for example your box has a 60mm male thread you would bore/turn the female or internal thread to 54mm, then cut the thread using the male thread as your final size gauge.

A little trick you can try is to lube the thread with a wax or even soap when finished to give a nice sliding feel as its done up. Some coat the thread with CA which hardens up the thread form.

But may require a final cut after the CA has hardened up, a down side can be brittleness to the threads and the liklehood of breaking with rough treatment.

The more coarse the thread the more likely you are to have some tear-out, at 5tpi its bit coarse but the up side is its easier to practice as the progess is more visible.

Timber selection is also very important, dense timbers such as Gidgee, lignum vitae etc, soft timbers like Pine etc are a nightmare. If you have to cut a thread in a soft timber, you may have to condition the timber with some very thing CA or some thing similar. But personally I would not bother, its just an excersize in frustration and patience.

Speed is important, especially when starting out, the slower the better. Two places for good info are the Sorby and Fred Holder sites, although his article seems to be missing.

Movies


Ceramics, would be a different kettle of fish altogether as it wont 'cut ' like timber. I think you might be on your own here. But in saying that, your ceramics would be very exclusive in thier design because of the threads. It might be an idea to include on your ceramic male thread a thin plastic washer or thin O-ring to bed the female thread onto as its done up so it wont rattle when together.

Probably it would be best done after drying and prior to firing and you could try turning the tool up side down for a final polishing where it wont cut, but rather glide over with a smoothing action.

I am currently making one for Cliff at 16tpi, pm me if you are interested. But in the meantime give yours a sharpen, on the top only dont be tempted to touch up the grooves and remove all the burrs etc off the cutting edges. Best done by going over the ground area with a fine stone after a light grind, and do so till the ragged edge is clean and sharp.

[Cliff Rogers]

Good info.

[hughie]

I have been meaning to post this info on thread depths and core diameters for those who already have a 3in1 chaser.


This should take the guess work out of the ID of the female thread.

10tpi depth of thread 1.6mm therefore reduce the ID or internal diameter by 3.2mm

ie 50mm male thread, then the bore would be 46.8mm

If your not comfortable with the dimensions then round them up to 3mm and 47mm

16tpi thread depth 1mm therefore reduce the ID or internal diameter by 2mm

ie 50mm male thread, then the bore would be 48mm.

Cut or chase the male thread first and then do the female, fitting it to the male as you go.If your new to chasing go slow, take your time and choose a dense timber for your first time.
Much is made of it being 'a lost art' etc and the 'difficulty in chasing' etc But if you can master the bowl Gouge and the Skew you have nothing to worry about. Just a little practice and you will be up there with the best.

To measure the diameters I use an el cheapo plastic digital vernier, works well

I am currently doing a couple of 16tpi for forum members and if anybody is interested I can include them in this run. I anticpate to have this batch complete and delivered before Christmas, just pm me.