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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: Making a small profile tool.
02/05/2017 10:04:23

About 18 months ago there was a thread where pre-insert threading tools were discussed. This is an alternative to the tangential tool design above that may be worth consideration. The tools discussed look like this.


It should be quite easy to produce a disk in gauge plate with the required profile, harden and temper it then sharpen the cutting edge. You can make a profile tool to create the disk by drilling a piece of gauge plate near an edge then cutting half of the hole away followed by hardening, tempering and sharpening. The advantage of this is only one tool body is required and a selection of discs could be made over time as the need arose. Larger radius disks may need a half profile tool to cut each side separately.

Martin C

Thread: Weird mill problem.
01/05/2017 22:40:58

If you are moving 15mm based on the scale on the handwheel then moving back 15mm based on the handwheel scale what you have is backlash. The point of the DRO is to allow you to make movements using the DRO not the handwheel scale. Backlash is not usually a problem on a lathe as you only work from one direction.

Is this what you are doing?

Martin C

Thread: Unrecognized gauge marked "PERLES"
01/05/2017 18:34:32

Bead, pearl,  stone gauge.


Martin C

Edited By Martin Connelly on 01/05/2017 18:35:06

Thread: Which is the best diameter for an ML7 Leadscrew.
30/04/2017 18:44:44

With a bigger diameter the load on the thread surface will be over a larger area. Perhaps this reduces wear.

Martin C

Thread: Boring head then fly cutting - OK or naughty step
30/04/2017 18:38:53

It is said that the proof of the pudding is in the eating. If you have an acceptable result it falls under the "more than one way to skin a cat" category.

Martin C

Thread: metric thread on my imperial lathe
30/04/2017 08:51:41

As you cannot reverse the motor the safest option until you have used the lathe for a while is to do as Hopper says and disconnect the drive to reduce the force required to manually wind the tool back to the start position. As an alternative to turning the chuck if you can devise a suitable hand crank for the left hand end of the spindle it would be an easier job. If you Google lathe hand crank there are lots of hits that will show the idea and lots of reasons to make one. Just remember that it should not be in place when the motor is engaged and started.

Martin C

28/04/2017 09:31:40

Hopper, doesn't the selection of A halve the speed of the lead screw compared to position C to give 8tpi instead of 4tpi?


27/04/2017 14:28:32

Muzzer, the original question was about a left hand thread hence the requirement for a tumbler reverse or an additional idler gear in the gear train (which is what the tumbler reverse is).

Martin C

Thread: Oilon
26/04/2017 13:54:24

Nylacast have pictures of oilon components on their website that include gears so they think it is good for this purpose. If you have trouble getting small quantities at a low price I may have some scrap stock.

Martin C

Thread: metric thread on my imperial lathe
26/04/2017 10:10:00

Ok John, you have a method that works for you with your lathe. It will also work for anyone else who can reverse the motor on their lathe. Do you know if the OP can reverse the motor on his lathe? Everyone is saying reverse the lathe and don't open the half nuts but a beginner may assume that means using the tumbler gears. A lot of people have lathes that do not have a reversible motor, a lot of posts I have seen in the past are from people asking "why would they need to reverse their lathe motor" as they have never done it or needed to.

The OP was asking what was needed in the way of gears, that has been answered within reason from the information from the OP. The second part was how to do it. For a beginner the instructions need to be don't open the half nuts but also don't move the tumbler gears, If you don't have tumbler gears you need to put an extra idler in the gear train. If you can't reverse the motor you need to hand crank the lathe backwards and if you have a long thread to produce then you maybe should consider moving the carriage back 7.5" to save hand cranking as it could save some time and effort. Everyone is trying to be helpful but we have not been given what we could consider full details of the equipment available and the part to be produced because as the OP said he is a beginner. If we submit what is considered to be useful information the OP can read it, digest it and either comprehend what is being said or ask further questions and possibly submit more information.

Are you trying to discourage people from trying to help?

Martin C

26/04/2017 09:15:58

Further to the "don't open the half nuts" instruction.

If you have a long section of thread to cut ( I recently had a leadscrew that was 200mm of 2mm pitch to cut) you can open the half nuts and move the tool back by hand but with a big BUT in the method. You need to move a distance that has an exact number of inches and an exact number of pitches as well. For a 1mm pitch this is 5" or 127 pitches. For 1.5mm pitch 7.5" moves 127 pitches. If you have a DRO fitted then this is reasonably easy to do but I would not recommend it for a beginner.

The choice of to do this or not will depend on a number of factors such as how long the threaded section is and how fast reversing the motor is driving the saddle. If you can't reverse the motor then you need to hand crank the spindle backwards because you should not touch the tumbler reverse (has anyone mentioned this fact earlier?) because it can have the same effect as opening the half nuts and losing position in the thread.

The best instruction I can think of is photograph or sketch the change gears before you start changing the gear train setup to ensure you can go back to where it was before. Then practice what you need to do with some scrap until you are happy that you have got everything sorted out and you know what you need to do for a successful outcome.

Martin C

Thread: Home made polishing and deburring machine build
25/04/2017 13:19:01

Expect it to spit out pieces of wire. You may need more metal around it. Don't forget a workpiece support. Specs for a commercial version are here.


This uses wheels that are Ø250 x 60 so your specification may be a little underpowered. Do you have a wheel identified and does it have a max rpm on it?

Martin C

Thread: Hiring a model live steam chuff-chuff.
25/04/2017 10:36:14

Try this


Martin C

Thread: Modifying collets?
25/04/2017 10:30:23

MG's advice regarding slave collets seems like a good idea. If you are missing a few sizes and are going to use that size regularly buying something like that makes sense.

If you are only after occasional use then a soft/emergency collet may be the way to go. These have a number of advantages because if you make one 1/16" for example then if it gets worn make it into a larger size and make a new 1/16" one. Also you can use them like soft jaws on a chuck and machine them with a pocket. For example if you had a lot of washers to drill out to a larger hole size then a soft collet would make mounting and drilling them an easy task. Note a steel soft collet is only relatively soft compared to a hardened and tempered collet and can last quite a long time before wear starts to be a problem.

If slave collets are hard to find you could consider an ER16 (or other size) collet holder with a parallel shank to fit into a collet or 4 jaw chuck on your lathe.

Grinding a collet to 1/16" sounds like a problem, I would think annealing and drilling may be the best solution then you have the equivalent of a soft collet. EDM would also work if you had access to a suitable machine.

Martin C

24/04/2017 16:42:34

The way soft emergency collets are made to size is to have spacers in the gaps, put the collet in its holder (spindle position for example) and tighten it up. It is then bored to the required size. To do it with a hardened collet you would have to grind it instead of boring it. If you look at pictures of emergency or soft collets you can usually see the spacers in place. After sizing remove the spacers.

Martin C

Thread: Tool post grinding
24/04/2017 11:48:06

Does anybody know if a Dynafile/Dynabrade type machine has ever been put to use as a tool post grinder?

Martin C

Thread: Cutting Speed Table
24/04/2017 11:21:55

Richard 2

You may have no intention of getting into CNC at any point but it may be worth downloading Mach3 onto a computer. This has a wizard for speeds and feeds for milling included in it. It can be run in demo mode without a license (just select no device when asked when it runs) but the wizard works fine. Just make sure you have selected the correct units (mm or inches) in the config settings and close the program to set the units then start it up again.

Martin C

24/04/2017 11:04:32

Richard 2

To use the table that started this thread your cutter is Ø20mm and the material is aluminium. This gives a speed from the Ø19 line of 1006rpm. Consider this a maximum speed if you have a machine with enough power at this speed and choose something close to it eg 1000rpm would be fine but lower would also work.

What this table does not tell you is feed rate for milling. It is important to keep the cutter cutting not rubbing as earlier posts have stated. If we take the rpm to be 1000 for ease of calculation then we need to look at tooth load and number of flutes on a cutter. Let's go for a tooth load of 0.125mm or 0.005". First we can consider two flutes, this will give a count of 2x1000 = 2000 teeth per minute at the cutting point. In order to give a tooth load of 0.125mm we need to multiply the teeth per minute by the tooth load and we get 2000x0.125 = 250mm/minute as the feed rate. If we put the figures in for 4 flutes we get 500mm/minute as the feed rate.

So if you want to cut at the correct tooth load with a Ø20 milling cutter with 4 flutes you need to feed the material past the cutter at 500 mm per minute or 20" per minute.

Can you achieve this? It will depend on your choice of hand cranking, power feed or CNC on you machine. If you are hand cranking I think you should time yourself over a suitable distance to get an idea of the speed you need to go. Similarly if using a power feed you should find what speeds you get for the available settings. Using smaller cutters with higher rpm will require even faster feed rates.

One other thing about cutting aluminium is the risk of aluminium welding itself to the cutter resulting in built up edge. **LINK** This is why some lubrication is necessary and avoiding excess heat from rubbing helps.

Martin C

Thread: CNC controller problem
22/04/2017 08:14:34

I do not switch the motors on my vacuum cleaner or compressor on or off when I am running a CNC program because it always causes the CNC to freeze. This is an electrical noise problem. I think you need to move all of your motor wiring including its supply point as far away from the rest of the system as possible. I start and stop the mill motor manually but it is a vfd driven 3 phase. The switch for this is only a low voltage system and the motor runs up and down under electronic control without current surging in the wiring.

Is you motor wiring shielded? Is the motor power supply going through a spike suppression filter? These may help.

Martin C

This is the type of power suppressor I am thinking of. 


Edited By Martin Connelly on 22/04/2017 08:16:54

Thread: 3D printing step forward.
21/04/2017 16:56:36

Siemens printed turbine blade video. They do not have the life of the current blades but it will allow rapid development compared with the 2 years it takes at present to prototype and test new designs.


Martin C

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