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Member postings for Martin Connelly

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

Thread: help needed - wooden beam engine
16/12/2015 09:43:36

The beam is centred on its pivot with 3" either side to centre line of crank and centre line of cylinder. This means that twice the throw of the crank will equal the stroke of the piston. The cylinder is 1.3/4" long and the piston is 3/8" thick. Subtract the 3/8" from 1.3/4" and you get 1.3/8" left for piston stroke. If the crank has a throw of 5/8" then the stroke of the piston will be 1.1/4" with 1/16" either side for clearance. This means that 5/8" is the correct crank throw, no assumptions necessary.


Thread: Cutting Internal threads
16/12/2015 08:58:48

I have seen a picture of one on but that is all. It is possible to make something similar with a tap if you have one with the correct thread form but wrong diameter. This is a good reason to keep snapped taps. You can grind them back to one or slightly more than one pitch to get full form cutters for internal threads. I have a ground up 1" 8tpi tap that I use for cutting the threads to suit the lathe spindle I have which is 1.75" x 8tpi. I know the helix angle will be slightly wrong but if you raise the tool above centerline slightly it compensates. It is also possible to use it for thread milling if you have access to a CNC mill. If thread milling all other teeth on the tap need removing to just leave the one and a bit for full profile.

P Horn do end mounted inserts for threading with a similar idea to what you are after but they only do metric threads from 1mm pitch upwards as far as I am aware.


Thread: Collet Identification and info wanted please.
15/12/2015 18:13:24

I could convert to jpg format but there are 29 pages and it is probably best kept as one file. If someone has a web site that could make it available to anyone searching for collet dimensions for lots of manufacturers' machines that would be the best place for it. I have copied the Smart & Brown section to a single page made a new table with the data in it and put it in the files section of the Yahoo group for those lathes. It would be a lot of work to do that for all the other makes. As I write this it occurs to me that it may be something that could be put on the web site. I will ask Tony about it.


Thread: Formulae required
15/12/2015 13:39:29

Glad you have got this done. I have had a thought for the next time this needs doing though. If the required diameter is always the same at Ø75 then why not get something like a T slot cutter ground to the required radius so that it is a straight forward machining job? If you have a CNC lathe you could make your own tool since you are cutting brass, some silver steel shaped, hardened, tempered and sharpened would do it.


Thread: Collet Identification and info wanted please.
15/12/2015 13:18:04

I have dug out an old print out of the Crawford Collets products and scanned it to a PDF. There are 29 pages with dimensions and capacities listed by manufacturer so I was wondering if there was a good place to put this file or is it just a case of email it to people if they ask for it?


Thread: Myford rear toolpost
13/12/2015 10:02:16

File one side and pack the other to maintain the clamping effect.


13/12/2015 08:42:13

Grind or file the top of the parting tool. When it is turned over for the rear tool post it will be lower. Just avoid the area close to the insert to avoid weakening it.


Thread: Demagnetiser
13/12/2015 00:50:45

Why not feed the demagnetizer coil with the AC from another transformer? This will be a safe way of limiting the current in the demagnetizer coil and be more robust than a lamp bulb.

Thread: Gyro build problem
10/12/2015 14:25:41

A bicycle wheel makes a good gyro even though it has a low mass rim, it's just a large radius. Perhaps you could try removing material from the inside of the rim so you have a lower overall mass but keep the most effective mass, that is the mass that is as far from the centre as possible. also thin down the centre boss as much as possible, this is mass that is supplying very little gyroscopic effect. Finally drill holes in the outer ring to reduce its weight. It does not need mass or great strength.


Thread: CM10 Mill Gears
09/12/2015 15:22:09

Iain, if you look at the thread Postman Cometh Part 2 near the end Nick G. has a photo of a button tool mounted in a flycutter. It may be worth you trying this sort of setup. A small flycutter that can hold a 6mm square (or 1/4" square) tool and a Ø6mm button tool can be used quite satisfactorily for interrupted cuts. It does not require sharpening like a piece of HSS would, just rotate to a sharp edge or replace the insert as required. You will probably need a flycutter at some time if you have not got one yet anyway. Just don't go at it like a bull in a china shop, small depth of cut will do the job with time.

ArcEuroTrade and others sell a small set of flycutters with a Ø12mm shank that would suit a small mill.

Chronos sell 6mm lathe profiling tools (ref 773851)


Thread: Workshop anti condensation heater.
09/12/2015 14:57:45

I used to have a problem with "sweating" machines, usually after a cold night followed by a warm spring morning. When I needed to enlarge my workshop I demolished the old one and built all new. The concrete base was insulated with 3mm foam (for wooden floors) over a polythene membrane then flooring grade chipboard. I lined the inside with plywood and insulated the whole thing with 75mm rigid foam and have not had a problem since. No background heat, just a slow rate of change of the interior temperature when not occupied and a small amount of ventilation from the small gaps around the door.


Thread: Gas bottles
09/12/2015 14:32:00

What is the full bottle pressure? I would be wary of making an adaptor for this if I could not arrange a hydrostatic pressure test on a home made adaptor before using it with gas. I have seen brass fittings blow apart on a CO2 extinguisher system when the pressure was put on them for a functional test of the system. Turns out the supplier had some dodgy brass with internal weaknesses and had not tested the fittings before selling them. Four of five supplied were scrapped this way.


Thread: Postman Cometh Part 2
09/12/2015 14:06:19

I have used a 6mm button tool in the same way for long parts in stainless steel where possible wear of a HSS tool would have been unacceptable. The part was curved but with an average width of about 30mm and had six Ø20 holes in it. the button tool worked well and had no issues with the interrupted cutting required.


Thread: Aluminium swarf
06/12/2015 09:53:12

You could try cutting back in sections then finish off the required profile in one go. For example cut just 1/2" (or other suitable small fraction of an inch) at a time up to 1.9" and down Ø1.6" to keep the swarf ribbons shorter then finally finish off the last 0.1", when the material removal rate will be lower due to the smaller diameter, in single passes.


Thread: Welding Help for Building a Printing Press
06/12/2015 09:44:04

Have you considered using heat to correct the error, after all this is what caused it. All welds shrink as the weld pool cools from freezing point down to room temperature and no amount of mechanical restraint will stop it. The forces involved are massive. Judiciously applied heat that creates a small weld pool in the correct location will pull the part back to the desired position. If you are likely to scrap the part otherwise it is worth some time trying this.

The other option is to try to relieve some of the tensions in the welds by normalising as Tony suggested but this requires taking the part to high temperature and holding it there then reducing at a controlled rate. May be hard to do correctly in a home workshop.


Thread: 3PH Speed control, what Pulley?
05/12/2015 13:23:29

Oops, you are of course correct, I'm mixing up the motor in my lathe (S&B model M) which is six pole with speed when supplied with 50Hz is somewhere around 1000rpm (speed plate figure without backgear and centre pulley about 3:4 ratio is 752rpm). The one I put on my mill which was 4 pole to try to keep the speed similar to the single phase one on it that it replaced having an rpm about 1500.


Thread: What is it?
05/12/2015 13:00:28

I've got one as well.


Thread: The Interesting Video Thread
05/12/2015 12:58:05

If you read David Clark's "The Practical Engineer" articles you will read about accidents and near misses that could have had a lot worse consequences. If they had been filming and someone got hurt you would never have seen the film. People just accepted injuries and death as part of the process. The biggest killer due to work is currently asbestosis due to people working in their own clothes with just a cloth cap to keep their hair clean. A lot of their own families have also died from the asbestos carried home. The good old days were never that good.

If anyone thinks we should go back to those days then think about having to go round to someone's house and telling them that their loved one has been killed in an industrial accident.

I work in an industrial engineering company and nowadays it's a big deal if someone cuts their finger. That is how I like it.


Thread: 3PH Speed control, what Pulley?
05/12/2015 12:41:12

Must be a six pole motor then, the natural speed of a 3 pole motor with 50Hz supply would be a small percentage below 3000.


Thread: Drilling holes in stainless
05/12/2015 12:27:30

Where I work we drill 316L stainless pipe everyday up to 100mm diameter with hole saws, a lot of sizes with broach cutters (trepanning cutters) and smaller ones using coated stub drills Ø3 for pilots and then step up to the finished size. It is always done on a large Richmond or Asquith radial drill (the morse taper is M5 so that gives an idea of size). It is always drilled with power feed and about 0.1 to 0.2mm of feed per rev. Cutting fluid is sometimes but not always used. The speed is not important as long as it is not too high. Slow speed usually gives higher torque which is good but the power feed is essential. If you work out the feed rate required for manual feed with high rpm it will probably be far higher than you would expect. Constant pressure as earlier posts have stated must be used, do not dwell or work hardening will occur. This is where power feed helps. If you back off for peck drilling you must back off fast and far enough to avoid work hardening and then go back with the feed rate needed to make sure you cut on contact without rubbing. CNC makes this sort of task easy but with practice it works with manual feed. Its a bit like the problem of parting off, you need to have confidence and go at it without trepidation.

When screw cutting use a larger drill than the standard tapping drill. The material is tough so a 70% thread will usually be as strong as needed and the tapping process will be a lot easier on your nerves and the taps.


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