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Member postings for Jim Greethead

Here is a list of all the postings Jim Greethead has made in our forums. Click on a thread name to jump to the thread.

Thread: Quality of Engineer's squares
07/01/2012 00:08:49
" Another absolute method is to make 3 ordinary squares but with hinged blades . By testing them all against each other on a straight edge and adjusting so that they all touch full length on the blades in any combination you end up with three perfect 90 deg squares ."
 
Thank you Michael, that is a great refinement on my thought about the three squares. Three steel rules - the ones with the holes in the end - for the blades, a bit of flat rectangular stock and some work with the slitting saw and Robert is your father's brother.
 
And no filing (sorry Terry)
 
Sounds like a plan
 
Jim
 
Thread: Hot Air Engines
06/01/2012 19:32:02
Here are some Stirling powered boats Dick (you have probably seen them):
 
 
One of those blokes might be a good contact.
 
Keep taking the medication
 
Jim
 
Thread: Quality of Engineer's squares
06/01/2012 19:19:23
Michael: Your method of making a 3-4-5 square sounds like a good use for a bit of ground bar salvaged from a printer or copier. And there are other sources of cylinders that are accurate in diameter over sufficient distance; some drawn pipes might serve. Sounds like a job for a time when everything else is going wrong and one needs a break.
 
Terry: Thanks for the encouragement; when I did a Tech course a couple of years ago, I was obliged to file the usual drill gauge etc. and surprised myself by being able to do it. Filing a square is another order of accuracy but using your advice, I think I might be able to do it.
 
I did think about clamping the worst of my squares to the milling machine and taking a light cut. But of course, that would only make it as accurate as my mill.
 
All the discussion about cylindrical squares set me thinking (oh no!): flat plates are made by testing three against one another. That should work for three squares shouldn't it? Of course they would have to be set on a flat surface. The good news is that you would end up with three really accurate squares and could sell the other two.
 
Just a thought
 
Jim
 
05/01/2012 21:57:52
Michael, Terry,
 
With my hand skills, I would have a very thin square at the end of that exercise. But I guess it would not hurt to practice on an old square that is already stuffed.
 
Might give it a go.
 
Jim
 
Thread: Hot Air Engines
05/01/2012 20:12:16
Hi Dick, nice to see you still active (and complaining).
 
Your mention of the rolling seal reminded me of the Tailer Thermal Lag Engine in which Tailer used a small inner tube as the seal.
 
It might be a bit off-topic since the Thermal Lag engine is (arguably) not Stirling but the patent application is worth reading for the humour in it - yes, humour - unusual.
 
The patent is US patent 5,414,997 by Peter L Tailer for a Thermal Lag Machine. It is dated May 16 1995.
 
Cheers
Jim
 
Thread: Quality of Engineer's squares
05/01/2012 19:56:34
Interesting. I don't recall seeing specifications before like those in the reference URL but if they refer to the accuracy at the end of the blade then they agree with measurements I took the other day of the squares in my workshop.
 
At the time, I thought the squares were of low quality, expecting better then plus/minus 0.02mm but it appears that they are suitable for purpose.
 
Jim
 
Thread: SS Great Britain
04/01/2012 19:02:48
PS Waverley has a similar engine running on steam and driving the vessel (if funding continues).
 
A couple of years ago I was over that way and visited the Great Britain (fascinating and beautiful) and then took a trip "doon the wotter" on Waverley - a great combination.
 
So if you are looking for an engine to model, you could do worse than to contact the Waverley people who, I am quite sure, would be only too pleased to assist.
 
Jim
 
Thread: Laser centreing
04/01/2012 18:55:25
Good one Billy, I should think that the eye is capable of centring the punch mark (or whatever) within the circle to at least 0.02mm - it is very good at that.
 
I made a centre finder using a webcam a couple of years ago but had great difficulty aligning it on the axis and along the axis (not coning). Eventually, I gave up when I realised that the resolution of the webcam would not allow me to resolve 0.02mm because there were not enough pixels in the window.
 
When last I checked the laser pointers, they were not sufficiently accurate either.
 
But I must check MEW 186 and think about Billy's brilliant scheme.
 
Thanks to all for the input to this thread which is very illuminating (Ha).
 
Jim
 
Thread: Blacking
03/01/2012 01:39:48
Incidentally, all the blacking on this engine: http://www.youtube.com/watch?v=o-zo52flDbI&feature=related
was done with the Blackfast.
 
Jim
 
02/01/2012 21:30:01
I prefer to avoid heating the object but if anybody wants some suitably dirty oil from a Fergie, I am prepared to swap a sump full for some clean stuff.
 
Jim
 
Thread: Seig X2 Self-releasing Drawbar
02/01/2012 21:25:53
I just had a look at the HM45 and I think it might be possible to rig up something similar to the top cap (or at least performing the same function).
 
It would just be necessary to retract the quill and lock it before unscrewing the drawbar.
 
Hmmm...
 
Jim
 
Thread: Wheels from the solid
02/01/2012 21:21:42
That's a lot of hard work Neil and it is at times like this that CNC looks attractive; it must be wonderful to do all the hard work in comfort and then watch the machine do the donkey work. Ah well, maybe next Xmas ...
 
Jim
 
Thread: Video of tiny V12
02/01/2012 09:15:11
Beautiful machining - I have to hand it to people who can make 12 of something and have them all look the same.
 
And the video is something to which we all should aspire. It is worth watching over again just to see how he did it.
 
So it runs on air? Who cares; it is a lovely job and I got pleasure from the posting so thank you John and thanks to the blokes on the motorcycling site who recommended it.
 
My bikes are only twins: Bonneville and Honda CB350. Do I need a four?
 
Jim
 
Thread: Milling Cutter sharpening
02/01/2012 08:50:48
Does anybody know of a similar sharpening service on the east coast of Australia?
 
Jim
 
Thread: Wheels from the solid
02/01/2012 08:47:52
Good photo Neil and the wheels are coming on nicely.
 
You mention using the lathe; how did you leave the counterweights (or are you doing something sneaky).
 
Jim
 
Thread: Seig X2 Self-releasing Drawbar
02/01/2012 08:35:11
How does this work Neil? Does the top cap just press on the thick washer when the drawbar is unscrewed a bit? And do you have to let the spindle fly up to knock the drawbar loose?
 
Jim
 
PS I still have not made any progress with the "spanner/hammer" - just have to wait for the right size tube spanner to appear in the shop.
 
Thread: Blacking
02/01/2012 08:24:32
This is the stuff I use: http://www.blackfast.com/
 
A friend in Queensland is still using some that he purchased so long ago that the distributor has moved twice since he bought it.
 
It comes complete. The concentrate, the small pails with lids to keep the diluted chemicals and labels on each of the pails. Full instructions included.
 
I keep mine in a plastic tub and just drag it out and use it when needed and then toss it back in the tub and put it on the shelf.
 
Jim
 
Thread: Yet Another Tangential Tool Holder
01/01/2012 22:03:50
Thanks Billy, might be time to have a look at that Brunel cutter although I don't have any broken carbide drills or milling cutters at present. On the other hand ...
 
Chris: Thanks for the source of carbide. And what you say about angles makes really good sense. When I researched (flash word for googled) the various angles recommended for HSS tooling for different materials, every source seemed to track back to the work done in the 1930s by Taylor who, as you say, was trying to optimise the production of components.
 
As I recall, he established a lifetime between sharpening for the tool and then changed the angles to maximise the volume of metal removed during that lifetime.
 
As hobbyists, we are not so concerned about tool lifetime in that sense but there might be tool geometries that give better surface finish on different materials - like backing off drills for brass etc.
 
Jim
And 'ave a good 2012
 
Thread: Help with poor finish when cutting with the side of the cutter
01/01/2012 21:52:00
Hi Nic,
 
Thanks for the link, I did read all the way to the finish. He decided that the problem was that the taper was bellmouthed and that the solution to this (and other) problems was to have the spindle rebuilt.
 
But then we did not get the results from all that. A recent post has asked for the outcome so we may yet find out.
 
BTW, I get this type of finish and I also get it when I use a woodworking router bit to round off the edges of my engine bases. The bit is a two blade carbide so I was not surprised to see chatter marks. But perhaps it is just the limitations of the HM45.
 
I will be interested to see the results you get with the carbide end mill.
 
Jim
 
Thread: Yet Another Tangential Tool Holder
01/01/2012 10:10:05
Thanks for the tip Chris, obviously solid carbide is not too brittle in this mode. Can you recommend a source?
 
Happy 2012 to all
 
Jim
 
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