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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: 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

Thread: What port
01/12/2015 13:40:52

I would think the feed in inlet will be into the valve chest chamber so that the pressure pushes the slider down onto the face with the three holes in it. If the holes are A B and C then the slider should move so that in one position it links A to B to exhaust the end of the cylinder connected to A. In this position the inlet pressure in the chamber is linked to the other end of the cylinder at C. This will push the piston from the C end to the A end of the cylinder. The opposite end of the slider travel links C to B to exhaust the C end of the cylinder and at the same time exposes the A opening to the inlet pressure to move the piston from the A end of the cylinder to the C end of the cylinder. B is exhaust to wherever it is meant to go, condenser or atmosphere. The valve gear times the opening and closing of the ports to pressure or exhaust as necessary to create the motion required of the piston.

Animation

**LINK**

This animation shows a slide valve in motion. Inlet is top centre, exhaust is bottom centre.

Martin

Thread: Drilling big holes in 304 stainless steel
25/11/2015 12:00:55

Where I work we drill a lot of holes in austenitic stainless steel pipes. All of the larger drills were blunted at the corners and produced nasty rags on the inside of the pipe. When I investigated what the problem was it turned out that almost all of the pipe fitters had been told to reduce the feed per rev (using a large radial drill) when using larger drills. This is completely the opposite of what you should do. If you think of the cutting edge of a drill as a chisel then it should be obvious that there is a suitable angle to drive it in at. Too steep and there will be too much force required, too shallow and the chisel will skate along the surface. If you consider the right angled triangle formed by the circumference of the drill and the feed per rev it should be clear that in order to maintain the resulting angle the feed needs to increase with increasing diameter. The damage to the drills and the rags on the inside of the pipe was caused by the drill pushing rather than cutting its way through the pipe wall. Correcting the feed per rev improved the life of the cutting edges and the time taken to deburr the holes. A suitable feed and speed chart stuck on the drill fixed the problem.

The feed per rev for austenitic stainless at 20mm should be about 0.21mm. If we apply this to your 20mm hole and a speed of 100 rpm on the lathe then we should be feeding the drill in at 0.21x100 = 21mm per minute. At 300rpm you would be going at 63mm per minute.

We then get to the question of to go up in steps or not. If you need to feed at 0.21mm per rev for 20mm what is this doing to the inner edge of the drill with say an effective diameter of 10mm. Well at 10mm the recommended drive is half that at 20mm so the feed is far too high for the inner part of the drill. Trying to push the drill through the stainless with a small pilot hole will probably result in a feed that is too slow for the outer edge. Small pilot holes and then drill to size may work with more forgiving materials than stainless.

In summary you should use the correct feed and speed for drilling holes and step up probably a maximum of 4mm at a time to ensure the cutting edge of the drill is doing its work as it is designed to work. Recommended maximum speed for 20mm diameter and austenitic stainless is about 350 rpm

It is also important with work hardening materials such as austenitic stainless that the tool never rubs as it will cause work hardening which will take some effort to get through without resorting to carbide cutting tools. Keep the pressure on or back off quickly to avoid rubbing.

If you get an ER32 chuck to fit your tailstock you can put milling cutters with shanks up to 20mm in it. If you get a three flute centre cutting end mill you can clean up the hole to its final size and get a flat bottom to the hole. I would probably drill out or end mill to 16mm before the final pass. Additionally the three flutes are stiffer than a twist drill and will give a better result than a twist drill.

Information on drilling feeds and speeds is readily available, search for drilling speeds and feeds chart images on the internet.

Thread: Jay Dee tapping heads
25/11/2015 09:57:30

Found this reference to someone who had picked one up at an auction.

**LINK**

He says there is a direct drive insert for drilling without removing the tool and then torque limiting inserts for tapping. So the question is do you have the drilling insert with the drive dog on the end inserted?

Thread: Gauge plate as bought
24/11/2015 11:27:19

It is supplied annealed and so is machinable. it can be welded but the heat affected zone becomes very hard. It can also be described as ground flat stock or tool steel. See WWW.RSWWW.COM for example stock number 682141 or WWW.BUCKANDHICKMAN.COM stock number 233833B. They give typical tolerances and BS standard numbers it conforms to. I was cutting some recently using a carbide end mill without coolant. Chips came off a nice blue colour without causing any problem for the 6 flute 12mm cutter and with a nice finish on the cut path. 25mm holes were put in (1/2" thick stock) with a broach cutter (trepanning cutter) and other holes drilled and tapped M10 without problems.

You may also find more information on **LINK** the Sheffield Gauge Plate Ltd web site.

Thread: Collet Identification and info wanted please.
23/11/2015 12:49:41

I would be interested in them for my Smart and Brown Model M.

Martin

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