Member postings for andrew lyner

The air that's gone into the room is still a 'potential hole', though and the air in the hole is now a new actual hole.

But this gets a bit tenuous when you put a brass threaded rod in the hole. I don't think you could now call it a brass hole.

Collapse of argument.

It just struck me that the thread title must be wrong. The hole itself is, in fact, made of of AIR.

@not done it yet: I get the picture now. Balloons are definitely not isotropic solids. They are kept inflated by the tension in the envelope balancing the internal pressure and Rubber definitely doesn't follow Hooke's law; it is very non linear when near its yield point so I reckon all bets are off when trying to analyse what would happen with your two balloons.

PS you would perhaps need a tube connecting the two air masses to balance out the pressure, I think.

Andrew

It's amazing that such a soft substance could be so problematical. I have found that drilling a, say, 7mm hole direct, I suddenly get resistance against the cut as if the drill is pushing against something hard. Not at high speed and no 'hot smell'. A small pilot hole seems to help avoid the problem.

Absorption of water would only affect the surfaces as it would take years, probably, for water to permeate throughout the plastic. I'd imagine the treads would swell 'into' the hole but the body would stay much the same size.

Coopers work on the principle that everything gets bigger when you heat an iron hoop - including the hole.

(I didn't get the balloon bit. Sorry)

I had some success with this. I just squeezed the work in a vice and re-tapped, as advised. The screw, which is for adjustment, is now finger tight. I suspect things may swell up again because there will be oil around. But I can re-do the tapping so I am happy. I have also ordered a bit of Delrin to see how much easier it is to work with.

This has been yet another rewarding experience, helped by the 'brain' that is ME's knowledge and skills.

@Neil I like the idea of boiling. I could try that with the existing part I'm half way through making.

Thanks. I will try Delrin and see how I get on.

I decided to make an M10 thread in a nylon block to take an aluminium screw.

The nylon is very tight, despite squeezing my M10 die in as far as it would go for the male thread.

Is there a bodge that I can do to loosen up that nylon thread? Perhaps some abrasive run between the surfaces - uo and down many times? Could I do something to the leading edges of an M10 tap? I'll try anything once.

I also (not surprisingly) have been getting stringy edges and rings of nylon which I have to tear off. I have tried various tool shapes and I have read that slow and as sharp as possible is the right way. But, at the moment, the results are all a bit random.

Edited By andrew lyner on 25/11/2019 16:43:02

Yes. I saw that table design. That would probably be more useful than just buying an angle plate (I spotted that in my trawl through Chronos etc..

The vertical milling table I bought is the standard one afaics. It's pretty sturdy but the cross slide movement will not allow it to present along the line of centres.

I am learning that there are many perfectly acceptable 'bodges' in this work as long as you use your head and don't try to eat too much at a time. They tend to take a lot longer to set up than what you can buy. That seems to be the main drawback. I guess it could be different if the lathe were a proper workshop size, doing workshop type jobs,

The recommended cutting speed for aluminium implies that a fly cutting tool will be spinning at a truly scary rate. OTOH, too low gives its own problems.

I have a length of the dovetail already but the SW Equinox ED80 has a very short length of tube between focusser and retracted dew shield so it has to be stood off from the dovetail. the shape of the dovetail extrusion is quite cleverly arranged to take a range of radii but I cannot take advantage of it. Also, that short length of contact would appear to require a nice big contact area (the two M6 screws in the tuber are only separated by 13mm or so which makes it all a bit ' sensitive' if the whole setup is to be nice and tight yet minimise stress on the tube.

It beds in really well to the radius I've made. It should 'do' I think. I must see how the star trails look.

OH boy - you have to use an album. Still it does work.

Whoops. That picture didn't post. I just tried copy and pasted it in. I could see it fine on my copy as I edited it. I'm looking for an option to insert an image but the window I get is gobbledegook. I need a file select window and there doesn't appear to be one. Any ideas?

I trip out when asked for a URL. That's something from the dim and distant past afaic.

Edited By andrew lyner on 14/11/2019 23:28:18

This is how I did it. Same idea as @JasonB's The work piece had a hole in it and sits on the tool post. There are no T slots on the mini lathe cross slide so this seemed to be the only way to clamp it.

I re-purposed an 8mm drill for the cutting tool

It was all firm enough and I was using about 300 RPM with small nibbles.

The result is not bad at all. Right curvature, fair finish and in the right place!!

I guess I could make a fitting for the cross slide with T slots but that would be hard, I think. Is there anything available on the market?

Thanks for all the input chaps.

That's what I had sketched out and just the result I want. Thanks.

My table is vertical and not as firm but I could go very slowly. There is screw adjustment that way. Did the feed in the picture use changing shims? Ah yes - feeler gauges - smart. Fitting to my cross slide could be hard;

Is that between ctrs bar something to buy? Could be expensive so it would have to be DIY. I was wondering about the problems of holding the tool and making a square hole but I guess a round hole and a round/square insert would be doable. Was thinking to cut a slot in the bar and sink the tool in it. Strong enough if the bar is solid enough I suppose.The picture doesn;t show the tool clamping unfortunately.

IF I could get hold of a 90mm grinding wheel, that could do?

I have an 80mm refractor telescope which came screwed with two screws to a bracket that has a dovetail foot. I replaced the foot with telescope rings to make it all firmer. But now I need a lighter system and seem to have lost the original bracket.

I can do the dovetail and the rest of the bracket but I need to produce a nice clean 45mm radius groove along the top of the bracket (around 30mm wide) to sit the optical tube in. I have a milling table for my mini lathe and was hoping to mill a long internal radius slot along the top of an aluminium block.

A fly cutter with a long arbor could do the job but the lathe is a bit flimsy IMO. I was thinking I could use a long sort of boring bar, supported at the tail stock end to hold it steady and use a flying cutter (carefully).

Alternatively, I could try to form a flat plate round a suitable pipe to get the curve and sit it on top of my bracket.

This is the sort of thing I could imagine would be needed to fit a cylindrical boiler for a steam engine so people must have already solved this problem. Problem is to choose the best search terms for information straight from the internet.

Any ideas?

Edited By andrew lyner on 04/11/2019 17:34:53

Many thanks for all those thoughts from everyone. Much appreciated, as usual.

I did consider the Three Plate method aamof, as it was mentioned in the Optics part of my Physics degree course. The lecturer (decades ago) seemed to imply that it was done by ancient old technicians in long brown coats and that it took days and days (he was talking about optical flatness of course).

I guess it would have the advantage that I could sell one or two of the resulting plates.

A cheapish solution seems to be the way to go. After all, it I get more fussy as time goes by, I can always step up in cost and quality.

I have watched a number of YouTube movies showing how to improve the various 'flat' surfaces on a mini lathe. They mostly seem to involve a surface plate, which is not a cheap item.

What is the alternative? I do have a number of thick steel plates. Would that be a good place to start - or perhaps some glass? Failing that, I guess I could start with the 'best' surface that's on the lathe and use that as a reference. Is that easy to measure? I have a budget dial indicator to help me.

Many people must have improved their mini lathe performance. How have they done it?

Edited By andrew lyner on 21/07/2019 10:35:23

Yeah

I got it / them - I liked the thread lock tube picture best.

But I'm still surprised no one seems to have suggested turning up a suitable thread adaptor. An excellent exercise for the student one rainy afternoon..

I thought this was a "Yes we can" forum.