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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: 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.

Martin

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)

Martin

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.

Martin

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.

Martin

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.

Martin

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.

Martin

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.

Martin

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.

Martin

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

I've got one as well.

Martin

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.

Martin

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.

Martin

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.

Martin

Thread: 3PH Speed control, what Pulley?
04/12/2015 14:19:07

The worry for people using low speeds with inverters and 3Ø motors is motors getting hot. This is only likely to happen if they are running slowly and under a high load. The other worry is low torque at low speed. I would try using the motor at low speeds and see if it gets warm under normal operation. If it stays cool then don't worry about that aspect of slow running. As for low torque, if you are manually operating the cutting tool you control the forces on the motor, if it starts to slow down you will know straight away and can back off to get the speed back up. If the torque is too low to be used then you will have to revert to the slower pulley set-up.

In summary try it and see how it works for you.

Martin

Thread: CM10 Mill Gears
03/12/2015 14:50:32

Lots of end mills are able to plunge/centre cut. The mill manufacturers are not going to get into an argument about was the end mill in use flat bottomed or not so they just put a spec on the machine that covers all end mills. The ends of most are flat or very close to flat and the outer ends of the cutting edges are where most of the torque will be generated. A small degree of hollow grinding will not stop recutting of swarf or small particles getting in the gap and dragged around. A face mill is more likely to push swarf away from the cutting area than an end mill because there is somewhere for it to go.

Iain, the carbide inserts in the links you posted are zero top rake. Probably not designed for steel and a small hobby mill. If these are what you are using try getting some inserts with the same shape and size designed for steel and with a chip breaker edge and see what the difference is when they are used to cut steel. The flat faced inserts are designed to be tough for a long life but need a machine that is high torque and stiff to make good use of them. For a small hobby machine you want inserts that have "light cutting geometry" as Sandvik call it. The inserts really need to be matched to the material they are being used on.

Search on Ebay for TNMG and you will see a lot of inserts with a chip-breaker edge which will probably suit your machine better than those shown on the ArcEuroTrade site. I don't think the holes in the centre will be a problem for clamping as shown in your link.

Martin

03/12/2015 09:27:51

A face mill usually has inserts that only make contact with the workpiece at a corner or the bottom of a radius with the surface they are producing. An end mill has contact over the whole of its bottom face. This large contact area can produce drag or recutting of swarf so results in the reduction of max diameter for an end mill compared to a face mill. Also the face mill often has more cutting edges so the chipload is lower per tooth and the load on the drive train is not so variable, you get nearer to a constant torque and less like an intermittent cut.

Using the mill at its maximum size of 10mm for an end mill or 20mm for a face mill is like running any machine at flat out, likely to find a weak point and cause failure. These machines are made to a price and not for industrial use. Keep away from using them at their specified maximums to get decent use out of them.

Martin

Thread: Screwcutting aluminium.
02/12/2015 14:06:38

Have you got an old M10 tap that you can grind up. If so you can make a thread chaser for 1.5mm pitch threads from it. I have done this with other sizes and have used them for CNC thread milling as well. They are not perfect for an external thread form but the difference is very small. You could probably use one for cutting the thread as well if you grind away all but one and a half teeth on one land. Make sure you are keeping full teeth, not ones in the tapered part of the tap.

Martin

Thread: CM10 Mill Gears
02/12/2015 12:52:13

The specs for the CDM10 mill include end mill capacity of 10mm. Using a 19mm cutter that is close to double this diameter puts double the torque on all the gearing and results in double the force on the gears. This will break the weakest part every time. There is a reason the max diameter in the specs is 10mm, don't overload the drive train by trying to use the mill beyond its capacity. Since Ø10mm is the maximum you may be better off using something like Ø6mm and accept the limitations of the machine you have in terms of speed of metal removal.

Martin

Thread: metric 123 blocks??
02/12/2015 12:46:17

I bought some individual Mitutoyo gauge blocks in May.

611675-131 50mm £33.67 +vat

611635-131 25mm £25.12 +vat

Just letting you know the cost if you go this route.

Martin

Thread: Turning 304 stainless
02/12/2015 09:55:38

2015-12-02 09_41_36-uk monowheel team.jpg

This is one of the parts in stainless that I made for the UK Monowheel Team's record holding Warhorse. See their facebook page for further details. (Welding by someone else)

Martin

02/12/2015 09:51:46

If you look at drilling tables for stainless steel you will get maximum speeds and recommended feeds. If you are using HSS tooling these figures can be used with a workpiece in a lathe. For example a Ø25mm drill should be run at a maximum of 235rpm and this figure should be used for a Ø25mm workpiece. If using carbide tooling then higher speeds can be used but double that for HSS is probably a safe guide. The feed per rev is very important for stainless. I use about 0.2mm per rev (CNC setting makes it easy) so you will need to find something similar to this if using power feed on the lathe. Hand feeding runs the risk of dwelling and causing work hardening. If you are doing 500rpm then the feed rate works out at 100mm per minute. This is may result in manual cranking at quite a high rate so slower revs may be important for manual operations.

Depth of cut is often critical, especially when using carbide. I try to stick close to 0.2mm. You need to work out what will get to your desired diameter using steps of about 0.2mm with a regular checks as you approach your target size.

I have a 25mm paintbrush which is well soaked with high sulphur cutting oil. I keep this on the workpiece to apply a thin film of lubricant and to keep small particles of stainless away from the cutting action.

I use carbide insert tooling with 0.2mm radius tips

Martin

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