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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: 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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