Newbie trying to thread

Gents,

After reading Brian Woods book on the 33t and 34T threading possibilities for the Myford S7 I made the drop arm required to lower the banjo slightly and set up to cut a thread. Work piece was supported by a half dead center.

I had a go at an M10 x 1.5 and the results were terrible, I couldn't even call it a thread. More like a train wreck. This is what I did. Please let me know if my thinking is on the right track here.

Half nuts left engaged the whole time. I used the "jog" function I have and took a first pass which conformed 1.5mm pitch. I then reversed the machine and dragged the tool over the first thread. This buggered everything up. Was this because of backlash in the gear train? Should I have retracted the tool first, then reversed everything, moved the tool back in and only then taken another pass?

Am I right in assuming that you can't just reverse a gear train set up and expect the tool to pass over the exact same scratches you just made?

Sorry for the silly question, all help is much appreciated,

Mark

Hi,

If you reverse the direction you cut a left hand thread!

So no, most definitely not.

Don't be too upset with yourself though, it isn't that intuitive!

Regards.

David.

I should have said that apart from not withdrawing the tool,the method is correct.

Take small cuts rather than trying to do it in one or two passes.

David.

Hello Mark,

As David Colwill says above, withdrawn the tool so that any backlash in the gear train has no effect on the thread you are cutting.

For the next pass, put on a little more feed and take the next cut.

If you want to see the effects demonstrated convincingly, put a Sharpie marker in the tool holder instead and pretend you are using that to cut a thread, only this time do it as you described for your train crash. You will see the displacement that backlash introduces.

I hope that helps Brian

David and Brian, many thanks, I will persevere and report back. I’ll try and cut an M20 in aluminium just so I can a little better at what is happening.
Thanks again,

Mark

The first time I did threadind was a complete train wreck too. The easiest way to learn is to watch YouTube vids on the subject.. As David said withdraw the tool fom from the thread reverse beyond the start then reset for the next cut keeping the half nuts engaged at all times. The reason you dragged across the first cut is because of back lash in the lead screw

MickyT

Micky, many thanks, yes that must be it indeed as Brian and David also said.

Upwards and onwards!

Mark

If you want to see how much backlash there is in the whole gear train, leadscrew and half nuts system then move the chuck both ways by hand to see what is required to reverse the carriage movement.

By the way, unless you have tumbler gears and operate them you are not cutting a left hand thread. The reversal of the spindle also reverses the leadscrew. The result is a right hand thread regardless of the direction the spindle rotates. There are just two helical scratches with some angular difference between them due to backlash but they are both a right hand helix.

Martin C

Hi Martin,

Correct, I wasn't cutting a left hand thread on the way back for the reason you state. I was messing up the right hand thread on the reverse pass.

Mark

Gents,

I took all of your advice to heart and had another go today. Total succes, even pleased with the fit. This is not a functional part, merely a test cut to validate Brian Woods drop arm and 33T/34T set up. Worked like a charm.

Thanks for all the tips,

Mark

Good job!

Tony

I am glad you have posted this, because i bought the 2 gears. Never got round to trying them, but what is it I have to make, (Drop arm or something. Confused as to exactly where the 2 gears go. I have read a lot about this subject but not sure i ever saw which gears to change. Any pics would be much appreciated.

Steve.

Ahh,

Sorry about the left hand thread bit. The lathe I use for manual threading has a dog clutch arrangement, when I reverse it I am operating the tumbler reverse and not the motor direction.

Good job on the thread though.

Regards.

David.

No worries David, I am not at the level to have properly understood what you said anyway so no harm done. Thanks anyway though.

@Steviegtr this is the wheel to place the 33t or 34t gear. Because it is a bit bigger than the gear normally in that position you have to drop the banjo a little bit lower. This means you have to make a simple drop arm.

That is a pic I borrowed off this site. I'm not sure who's it is and all I did was added "this one" to show the appropriate gear.

Mark

That pic of your early success looks as good as one might hope for, with later successes! Spot on!

For my first threading attempts, I typed and printed out a list of successive actions for a complete machining cycle, so that I did not mess up by missing one operation. Never needed it after about the second run down the thread but I reckoned it helped to make me remember it!

You can now start with a larger piece of stock, turn it down and thread it, then make the other end into a hexagon for any bolt of desired size. Or save material by making the shank and head separately, then welding them together.🙂 Done that before now, to match large square headed plough bolts.

Yes, very nice job indeed.

Mark, looking at your picture I would like to make the following observations. The thread looks good but the tool looks to be stuck out a bit more than i would have it and if you dragged that carbide bit backwards over the workpiece you are lucky if you didn't chip the insert.

If you can then reduce tool overhang as much as possible. If you run a carbide insert backwards then always inspect it carefully if it hasn't snapped or obviously chipped from the upwards force on the edge.

Martin C

Yes to both questions - that's exactly what happened and that's the way to circumvent it.

If you're plunge-cutting the thread (as distinct from half-angle) you'll usually have to reduce the depth of cut after the first one or two passes, so that you don't get two substantial chips colliding on the top face of the tool.

Ah, looks like I'm way too late. Nice job.

Edited By Mick B1 on 05/06/2020 09:18:26

Martin, good idea. I have not examined the insert yet but will do that, thanks. I will also pull it back into the holder a bit more. No reason at all for the over hang.

Mick, yes this was a plunge cut. I used copious amounts of oil As you can see in the photo but will cut them at the proper angle once I have discovered how to accurately establish the 29,5 deg recommended for a Metric thread. Thanks for the tips,

Mark