Member postings for Rod Renshaw

Oil blackening is a traditional process. It's in all the old books - "heat to red or nearly so and chuck it in old, used oil, the older the better." Lots of fumes so do it outside. If the parts are small and there is plenty of oil it won't (usually) catch fire, but be prepared that it might.

But times change, engine oils and petrol now contain additives, who knows what the fumes may contain, we are more aware of the risks, best avoided.

Vegetable oil works okay and won't be as potentially toxic, and many of us still harden/ toughen tooling in oil, so use that, but still do it outside - and the fire hazard is still there unless the parts are very small.

As has been said, any heating process may cause distortion.

Chemical blackening works, some makes are more durable than others. Some will only work on mild steel and not stainless, so you may need to check the one you choose will work on cast iron.

Any of these processes, heat or chemical, needs very good cleaning/ degreasing etc to get an even finish.

Rod

Milling produces vibration, much more than that produced by turning, and a solid, heavy stand can help to reduce this. Milling needs lots of accesories, vices, angle plates, cutters and jigs and everything else, again much more than turning, so lots of storage space is very useful. And if the storage of these many and heavy items is in the stand then that tends to solve 2 problems at once.

Rod

Antique fruit knives may have silver blades, which may be too soft for anything except cutting fruit. (Carbon steel blades were not resistant to the acid in fruits and stainless was not yet invented.)

Rod

I can understand the OP's frustration - why can a tool last for ages when cutting steel but not when cutting card, which is so much softer?

The difference is in the cutting edge which needs to be much thinner, ie have a smaller included angle, so that it will cut a soft material cleanly rather than just push it aside or tear it. A lathe tool might have an edge with an included angle of 80 - 90 degrees, so there is plenty of metal around and behind the edge to provide support.

A knife or scalpal blade might have an included angle more like 12 -15 degrees, so the actual edge, the only bit that actually cuts, is very thin indeed and gets little support from the bulk of the tool. The Japanese say that a sword edge is sharpened until it is "invisible", that is, until it is so thin it no longer relects light. I am not sure if this can be literally true but it does give the idea of a thin edge.

Also, after any use the edge will start to wear, and the effect will be more serious in the thin blade because there is so little material in the actual edge and it is soon worn away. With a metal cutting tool a little wear may not be so noticeable, the motor provides power and the steel being cut resists tearing until the situation gets worse.

Woodworkers have this effect too. A chisel is normally sharpened with an included angle of 25-30 degrees. But a worker in oak or an exotic hardwood may need to use 35 degrees. Those working in the softer woods can use as little as 17 degrees for a handheld chisel used with care (and not with a mallet), and may need to use this extreme angle to get clean cuts.

It seems pardoxical, but the softer the material being cut the sharper the edge needed. As has been said above card is abrasive and will wear knife edges quite quickly compared with, for example, knife edges used on meat or many vegetables.

Rod

A local craft woodturner could make replacement balls, to replace the ones that have lasted 60 years.

Rod

+1 for Jacks view. The article seems to be saying "they" have found that several different atoms give slightly different results and in due course there may have to be a reconsideration of what is the most useful way to define the second. It's happened before, but it seems unlikely that any non-specialist will notice any difference.

Rod

I was reading oven man's post and wondering about his experience of stainless steel cutlery going black, and then I got to the mention of dishwasher tablets.

My wife and I have a dishwasher but rarely use it - being just the 2 of us and having simple meals and being retired and Radio 4 listeners we tend to wash up after every meal with washing up liquid in a bowl. Our 40 year old daily use stainless cutlery is as bright today as when we bought it.

Rod

Hmm... The OP seems to be asking about making flat discs by trimming the edges of a rough blank with ordinary turning tools, something that can be done with the methods listed above.

"Spinning", as I understand it, is forming a bowl like shape ( or a loco chimney top) from a flat disc by pressing the rotating disc against a former using a smooth ended tool to force the disc into a 3 dimensional shape. This requires a lot of pressure and a substantial lathe.

Rod

Can't speak about Arc, but it is conventional to ignore the tang when measuring the length of a file.

Rod

Brian

Did you find some screws?

I have a few 10mm long ones, are they long enough, how many do you need?

Rod

I read somewhere that back in the day when the colour of "Cherry Red" was originally used as a description of metal temperature, most of the apprentices being taught would only have been familiar with the glace cherries they saw on the Sunday tea table. Apparently fresh cherries would not have been seen in industrial cities at that time.

Rod

I admire Joseph Noci's version of a toolpost drill, and think he is right about the power needed.

It takes the same power to drill a hole in the lathe as it does in a drill press, so many setups that are fine for small drills will be very under powered for larger drills or milling cutters. So if the need is to drill holes of (say) 6mm or greater, then a 1/2 HP motor would not be excessive.

Rod

Pgk

Hmm.. it's not a normal process AFAIK, but it should work if the process could be controlled. The thicker parts might be surface hardened while the thinner parts might be hardened (and brittle) all the way through. Difficult to get any consistent results on a small component I would have thought. On a larger object one might try local heating with acetylene, and then quenching, on those bits needing to be hard.

Rod

Some good ideas on tempering above.

I have tried boiling parts in water as Peter suggested but found the tempering effect to be rather small ( only 100 C ) and parts of any complex shape still broke. It might work okay on "blocky" shapes not subject to shock loading. The oven ( up to 250 C ) works better.

There are Youtubes on making simple muffle furnaces from baked bean tins and fireclay, and powered by a propane torch which should give more controllable results, up to maybe 650C, which might give a tough result rather than a brittle one. Might more consistent for the initial hardening, at a higher temp, as well as the tempering. Not tried this myself.

For occasional amateur use, the parts might work for a long time even if left soft.

Rod

Nigel,

Yes, now you have said Birmabright, I realise I have misremembered.

Rod

From memory, ternplate was used for the bodies of older Landrovers.

Rod

I think I read somewhere that rose bits were really woodworkers' tools.

Single cutting edge countersink bits, of which there are several patterns, cut mild steel without chattering.

Rod

All university chemistry departments used to have a glass blower, and many may still have one. They are real artists and can work glass tube into wonderful things, sometimes to meet someone's need and sometimes just for fun. If you can find one they would make you a suitable bulb for interest or beer money.

Rod

+ 1 for Peter S-H' s view in his post of 20.2.21 at 18.17pm, I like the variety of the posts on the forum, and discussion of the content is a useful thing to do from time to time. However it seems to me that the forum content is what the members post, there being only a few moderators' deletions, so the content is up to the members.

I had been under the impression that the forum was the MEW forum, judging from the content and Neil's input, now I know better. If others have formed the same impression for similar reasons that will have tended to shape the posts made, and perhaps also the members who choose to belong, a sort of positive feedback loop.

Those who want more posts about models can get them by making more posts about models to shift the balance? I can't see any issues for the moderators about that shift. And like when reading ME and MEW, some articles/ posts will appeal to some readers more than others. We get what we post.

Rod

Edited to make it clear which of P  S-H'  posts I was supporting

Edited By Rod Renshaw on 20/02/2021 19:15:22

+1 for Peter' s view. ( where is that "like" button! )

I accept that this is not a forum for politics, but there have been mentions on here of Facebook being involved in the workings of this forum in some way, so we have a legitimate interest in it's doings.

Rod