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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: How to identify M2 first, second and third tap
13/03/2016 07:56:52

Spotting drills are very stiff and if positioned slightly off centre will chamfer eccentricly, on a small hole this will show up visually. If you use the spotting drill first then it creates a lead in that the more flexible twist drill will follow concentrically. It is similar to using a centre drill in a lathe to start a hole on the spindle axis.


Thread: Carbide tooling
11/03/2016 14:30:43

Chuck key left in chuck!


Thread: Edge Finder
11/03/2016 14:24:59

As far as I can tell the latest edition of this book is from 2004. I think it is easy to forget how far the internet and such things as Youtube and online shopping have come on since then. There may have been instructional videos available then but finding them would have been hard. Want an edge finder, scour suitable magazine adverts and hope you can find a good one at a good price. There is a possibility that times have overtaken books such as this, it is far easier for someone to make a video, edit it and post it online than it is to write a book and try to put into words what needs to explained. Books start to go out of date the moment they are sent to the publisher, a video can be replaced very quickly and a web site edited daily if required.

Then there are forums like this one. Got a question? Get it answered (in lots of ways sometimes) within minutes. What did people do before the internet? They wrote a letter to a magazine, hoped it would get published and hope that the answer was supplied to the magazine to get published in the following edition. Or they joined a club or bought a book or went to the local library.

Books are just one way of obtaining information now. Any one book may have some small nuggets of gold buried in them, or not as the case may be, but they can now be combined with what can be found out via the internet. The information superhighway is here now and the problem may be too much information and we now have to sift through what we have to find what we want. I think new videos are added to what is available faster than anyone can watch what is already there.


Thread: How to identify M2 first, second and third tap
11/03/2016 13:55:39

I have some M12 spiral flute taps and the short thread length on them makes hand tapping easier than with standard taps due to lower friction between tap and workpiece, initial alignment is important though as Jason pointed out. They work well in lathe tailstocks as well as vertical mills, I use them with a tapping box and as Andrew said you get continuous ribbons out of the flutes as the thread is cut.

On a slightly off topic point if you look at thread mills for M2 size the maximum depth of thread that can be cut is often stated as 3 diameters. This can be taken as a guide for any thread that is being cut, anything deeper is probably not needed for screw engagement.


Thread: Inverters? Talk to me.
09/03/2016 15:09:48

I think it is a good application for a VFD. Many VFDs can be programmed with set point speeds so a simple switch would be all that is needed to go from full fan to low fan speed. I would suggest contacting some suppliers and asking for their recommendations.


09/03/2016 14:40:37

Shaun, some invertors can be programmed with set points so once you find the speed for low flow a simple switch will select it. I think if you speak with some of the suppliers they will be able to suggest a suitable piece of equipment for your needs. It seems to me to be an easily implemented application for a VFD.


Thread: Colchester 2500-too big for first serious lathe?
09/03/2016 14:29:11

Surely it can only be too big if it can't do small items or will not fit available space. Lots of postings say you can do small things on a big lathe but not big things on a small lathe. I think a lot of people with small lathes would like something larger if they had the space and money to buy one. It does not take much for a lathe to be too small, many modelers have problems with larger flywheels not fitting into their lathe's working envelope.


Thread: Repairing a 4 jaw chuck.
08/03/2016 10:57:11

I have a 4 jaw with cracks around what on my chuck are square recesses in the screws. The rest of the screw is in good condition so there is no problem using it at the moment. If it does start to be a problem it's nice to know there is a solution that is relatively easy and low cost. My suspicion is that the screw on chuck has been fitted or removed by a previous user using a mallet or hammer on the chuck key in the screw hole. Personally I try to avoid putting the chucks on so hard that they require impact forces to remove them.


Thread: Lathe Tool HEight Gauge
08/03/2016 10:39:25

See this thread for pictures of the tool.



Thread: Boxford A gearbox rebuild advice
07/03/2016 14:53:40

Ajohnw, the reason the tufnol gears outlast the metal gears is that abrasive particles can become embedded in the softer tufnol and so abrade away the harder metal gears. This is a common happening when soft and hard materials are in contact with each other and there is relative movement. Shaping and polishing mirrors for telescopes can be done by putting the polishing compound on a pitch lap's surface and moving the glass over that surface. The glass is removed but the softer pitch is protected by the abrasive that embeds itself in its surface. As this lathe looks like it was never cared for the lack of cleanliness that is required for this mechanism to occur seems very likely.


07/03/2016 10:36:12

John and Michael, if you look at the centre portion of the spindle gear where the tumbler engages there is clear evidence of wear in the photos as presented. The ends of the teeth in the one o'clock to 5 o'clock position look like they have been stripped off.

If a new spindle is out of the question but the general state of the rest of the machine is in good condition I would suggest it is a potential CNC conversion. A spindle index pickup and X and Z axis drive is all that is required to make a machine that can still be used for turning and screw cutting. The gear driven drive train is redundant when such a conversion is carried out.

If you think this is beyond what you want out of a lathe you should be aware that by using manual data input (MDI) you can drive a CNC lathe just like a manual lathe but without using the drive train or turning handles to move the cutter around the workpiece. If you want to go further into what is available in CNC you would have the basic setup required with that setup.

If you think you want to stay away from CNC then maybe you could sell it as a machine that someone else could convert to basic CNC turning.


Thread: 'Hacking' an inverter
07/03/2016 10:20:15

The dealer has probably got away with this because most motors do not run at full rated power all the time. Who, for example, has a lathe cutting at maximum metal removal rate 24 hours a day? I agree with Michael W. Always get a bigger inverter than the motor requires, it may be re-purposed or the motor replaced with a larger one.


Thread: Trouble at Mill!
07/03/2016 10:12:21

I've had a conversation with an inspector that went:

The drawing states maximum gap of 0.5mm between the parts!.

They are touching so there is no gap.

There is a gap at the edge that is more than 0.5mm.

That is because the parts' faces are not flat, but they are touching so there is no gap.

There is a gap at the edge greater than 0.5mm.

Why is an assembly shop inspector looking at the part manufacturing drawing? What does the assembly drawing have on it?

Assemble the parts and check for leaks at pass off testing.

Then go and do that and when it fails that test come back and complain.

End of conversation.

He did not come back since the parts had already had a hydrostatic pressure test and had been passed off by the manufacturing department's own inspector. I think there are some inspectors who just love to justify their work and if they dig their heels in they take some shifting. I know one who I think was ready to claim that some stainless steel was no good because it didn't taste right when he licked it.


Thread: Lathe Tool HEight Gauge
07/03/2016 09:52:56

If you have an old hard drive that is scrap you can dismantle it and use the disk as a front coated mirror. The disk is aluminium and cuts easily with a junior hacksaw.

**LINK** for acrylic sheet


Thread: Aircraft General Discussion
06/03/2016 09:13:39

I saw a documentary that said the clipped wing improved roll rates, so that backs up JA.


Thread: Brain Teaser
04/03/2016 19:00:25

Gas fuel, liquid fuel, lubricating oil, air carbon dioxide are all transported by tube used in gas turbine packages. Rather ruins the idea that tubes are structural. Then there is scaffolding as used in the UK that is 1.5 sch40 nominal bore pipe. Purely structural and not used to transport any fluids except by accident if it rains.

Tube bought based on its imperial sized outside diameter and wall thickness is specified to plus or minus 0.005", I don't know the tolerance for metric OD tube. Nominal pipe sizes are based on ANSI standards and the tolerance on OD for sizes about 2" NPS is over plus or minus 0.06" if I remember correctly. Also nominal bore pipe has a minimum wall thickness but no maximum wall thickness, instead it has a maximum weight per unit length. This is a completely different way of defining the material from that used for OD tube.

Nominal bore fittings such as tees, elbows, reducers have dimensional tolerances of 0.06" and tube fittings match the tolerances of tube of 0.005".

It is because of these two major differences in the tolerances and method of specifying size that we differentiate between tube and pipe raw materials where I work.


04/03/2016 18:27:45

Sam L, pipe is available seamed or seamless, tube is available seamed or seamless. The method of manufacture cannot be used as a means of differentiating between what gets called pipe and what gets called tube.


04/03/2016 18:03:35

Where I work we refer to nominal sized pipe (NPS) as pipe and outside diameter tube as tube. They are both seamless. Once we make something from the tube or the pipe either by bending it or welding fittings to it the part produced is called a pipe (or sometimes a manifold). I think this is purely our own way of differentiating between the raw materials rather than something written in stone somewhere.


Thread: correct way to feed when milling
02/03/2016 10:39:31

I was milling some copper sheet this weekend. I was using the side of a Ø16mm 4 flute milling cutter to square up 1 edge about 100mm long so had the sheet held flat in the vice. I found that using climb milling the finish looked like it had been cut with a saw going hell for leather, not pretty at all. Went back over the edge with a small depth of cut and conventional milling and got a fine smooth finish. When set up to cut out a section to leave a U shape with the part clamped at all 4 corners with a Ø10mm mill conventional milling gave a rough cut and going back to climb milling gave a smooth finish. The point of this is that sometimes climb milling is best and sometimes conventional is best, it is all dependent on a lot of factors.

I think this item on the CNC Cookbook web site explaining climb versus conventional is worth a read.



Thread: Tailstock height
02/03/2016 10:04:53

I think you should check contact surfaces with some engineer's blue. A small high spot of 0.3mm may be doubled to 0.6mm at the point of the centre if it causes any angular error in the tailstock. These are not unreasonable amounts of material to remove with a file. Use of blue will let you see where there are high spots where material should be removed to maintain flatness. For this small error a milling operation may be a bit of "sledgehammer to crack a nut".


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