Member postings for Andrew Johnston

They're dead length collets. Looking at the size I'd hazard a guess they're for a 3/4" Britan repetition lathe. I don't think I have any for direct comparison as I sold the ones I had since I have a 1-1/4" Britan.

Andrew

If metric and imperial threading are wanted as standard, without a lot of faff, then one is looking at ex-industrial. My ex-industrial lathe cuts a wide range of imperial and metric threads via the gearbox, just swapping two change gears for the coarser threads. With an additional gear it also cuts DP and Mod threads. The only question is imperial or metric for the basic machine. My lathe is imperial so cutting imperial threads is simple, cutting metric tends to mean leaving the halfnuts engaged. And yes, I do know there are ways round it, but I don't do much metric screwcutting. For imperial I use an Ainjest threading unit which is very quick, no faffing with a thread dial indicator. That's another advantage of ex-industrial, there are accessories available that simply don't exist for hobby lathes.

For making bolt heads any cheap mill will do with an indexer. No point in paying through the nose for a fancy mill. Most of my bolts and nuts are made from hexagon stock, but for specials I use the vertical mill and the indexing plate on my dividing head. Mills like the Aciera are only truely useful with the accessories; and if you think Myfords are overpriced.....

Andrew

Correct, but I'll make a deal, you read mine and I'll read yours. Mine is mostly mathematics, associated with pulse compression radar signal design and Fourier transform processing.

It's magnanimous to fed us the constraints that you feel are sufficient, but if you're having to ask these questions I wonder how you know what is sufficient? Can you put some numbers on the requirements?

The sheet of 1050 is almost pure aluminium. Consequently it is very soft and horrible to work, by machine or hand, like warm fudge. It's basically useless except for low stress sheet metalwork, which is why it is only available in sheet form.

Andrew

PS: A copy of my Ph.D. is available for reading in the Cambridge University library, where is yours?

Edited By Andrew Johnston on 28/04/2022 21:06:35

You still have a lot to learn, even if you don't realise it. If I wanted work to be really flat and parallel I'd use a surface grinder after roughing on a mill. But of course the mag chuck only works with ferrous metals.

Andrew

It's interesting that rolled threads are used at the high volume cheap end of the market, but also in some critical applications. Note critical, not accurate; grinding is mostly used for accurate applications.

Andrew

I just knew someone would pop and say they have solid dies which work fine. Since the OP said he was a novice I was keeping it simple. Solid dies are not that common; the only ones I have are total crap, bought as a set online when I didn't know any better. The whole set (taps and dies) is unusable.

For external threads I tend to screwcut or use Coventry dieheads. I don't have the means to check threads to 6g and don't feel like buying go/nogo gauges, so I adjust to suit the mating part. This is what I expect a home made external thread (1/4" BSF) to look like:

The question about provenance has not been answered. If we don't know the quality of the die all other suggested solutions are irrelevant.

Andrew

Bin it; dies that are not split are either die nuts intended to clean up threads, not cut them, or they tend to be cheap and nasty. If the latter the die may be poorly ground and will never cut a proper thread. What is the provenance of the die? I don't use dies very often but have never seen the thread bent afterwards. I always use split dies.

Andrew

I made a plate similar to that by 'steamdave' from hot rolled steel for my hydraulic copy unit:

I've never seen a similar commericlal item.

Andrew

I suspect you'll be wasting time unless the material is fully annealed. If you remove one side of spring material it is unlikely to stay flat. Better to start with known material than waste time with unknown material.

I'd face something that size on the mill, but I have a large mill. Alternatively I'd use a 4-jaw chuck in the lathe. Depending upon the hardness/temper HSS tooling may, or may not, work.

Andrew

The internal atomic structure is changed, which in turn changes the dimensions. It may only be tenths but it is measurable.

Andrew

You don't buy drills just for the shank. Drill blanks are available:

Drill Blanks

With quality drills the shank is usually a thou or so smaller than nominal diameter, so drill blanks are better.

Andrew

It's a special cutter. If the circular pitch is rational then by definition the module will be irrational as it involves a factor of pi.

Andrew

Never heard of the method. I was taught how to use a slide rule in the third year at secondary school, after which they were never mentioned again. I still have my slide rule and know how to use it. There is an x^2 scale so square roots are direct reading.

Andrew

Just tedium with a round needle file.

If there is a sacrificial blank on the exit side of the real blank the burrs where the cutter breaks through can be almost eliminated.

Andrew

I assume the depth of cut isn't full tooth depth yet?

Involute gear cutters are designed such that grinding the front face of each tooth on a radius reduces the OD of the cutter but preserves the correct tooth form. To do so an indexing method would be needed. If the cutter isn't too blunt try giving each tooth face a lick with a diamond hone.

Andrew

Spindle speed of 250rpm is on the fast side, I'd be aiming for around 60 sfm. As setup 10 ipm gives a chipload of 3 thou per tooth, which is reasonable. Depth of cut is the full depth of the tooth; cut in one pass. Multiple passes just waste time and blunt the cutter.

Andrew

It is simply down to the choice of clearance added to the dedendum; 2.157/DP in the book versus 2.2/DP used by Steve.

In theory cutting forces when using a gear cutter are symmetric, so the blank shouldn't rotate. For larger diameter gears a positive method of preventing the blank from rotating can be useful, like the green clamp when cutting this 11" OD 6DP gear:

I use normal calculations for feedrates when cutting gears, based on a chip load of a few thou per tooth.

Andrew

Apart from using a non-standard value for the dedendum.

Andrew

That's odd; there seem to be a fair number of threads on the forum about fixing problems with newish machines?

Apart from the CNC mill all my machine tools are old and secondhand. To be sure I've had some issues. But they've been consumable items, like broken belts, or electrical, mostly to do with chattering contactors. I've had no mechanical issues, other than due to operator stupidity.

The CNC mill has had it's own issues, all electrical such as dry joints and poor quality connectors.

Andrew

The calculation for the OD is correct. The addendum is one over the diametrical pitch, so 0.1". In theory the dedendum is the same, but clearance is normally added. Common values are 1.157 or 1.25 divided by the diametrical pitch. Total tooth depth is addendum plus dedendum, so 2.157 or 2.25 divided by the diametrical pitch. The larger tooth depth is used for smaller tooth counts, but there is no hard and fast rule as to the changeover point. The tooth depth will be 0.2157" or 0.225" depending on the clearance allowance. If the cutter is old stock it should have the tooth depth for which it was made marked on it. If in doubt I'd start with a tooth depth of 0.2157"; you can always do another pass. But it's more difficult to add material. For scale these are 10DP gears:

Andrew