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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: Heatshrink sleeving as a heat insulator for valve handles?
26/09/2021 08:06:09

The ATUM range of heat shrink tubing should be better than standard as it has an internal layer of hot melt adhesive that would secure it to the surface it was on.

Martin C

Thread: cutting spur gears on a mill
25/09/2021 08:32:56

It's not an algebraic thing, it's a chosen thing. You could add height to the teeth and end up with a pointed tooth but that is both pointless (pun not intended) and poor practice as there is no strength in the pointed tip. It is also a redundant feature if the next tooth has already started to take the load before the pointed tooth has disengaged from its mating part. That then fixes the dedendum as a minimum of the addendum and as pointed out above by Andrew a small clearance is then added to the dedendum. Aiming for pointed teeth would require a larger blank and would therefore cost more in materials that were just being turned into waste and take more power to cut which costs in terms of energy use and then there is more wear and tear on the tools.

I've not done any clock making but from general reading I think clock makers have to apply their own rules as they may have small tooth counts on a gear. That means that the part above about the following tooth being engaged to take the load before the point disengages is less likely. This requirement for longer teeth would then become a requirement for deeper dedendums and undercutting of the tooth forms.

Martin C

24/09/2021 09:31:20

At work we bought in planetary gearboxes from the likes of Allen. When you looked at all the criteria they took into account to avoid harmonics causing issues it was very complex and best left to the experts/specialists.


Martin C

23/09/2021 07:49:25

The ancient Egyptians had armchairs.

Martin C

Thread: Back to Imperial
22/09/2021 16:13:04

I spent a few years in my youth working behind a bar where the glasses were the oversize straight type with a line but they didn't have the crown or the words "Pint to line" or whatever the wording was since they were rejects (read cheap). We just filled them so the beer was over the line and with a head on top. Then they introduced measured half pints for Guinness. That, as I am sure you all know, takes an age to settle but we started to get complaints to the point where some of the bar staff had a pre-poured half under the counter to top it up. Where I worked has been demolished now but it was a venue where the Beatles played a number of times in the sixties.

Martin C

Thread: cutting spur gears on a mill
22/09/2021 08:38:35

I think trying to use free hobbing for a quick way of making gears is going to be a case of more haste less speed because of the crap it will produce trying to get a usable end result with desirable features. You will soon get to the point where value for money (and time) makes it a waste of time. There is a reason that after the centuries of people making gears it has never been a major method of production. this thread is a reflection of this and should be closed as trying to explain the problems to the OP is best described as flogging a dead horse.

Martin C

Thread: Back to Imperial
20/09/2021 17:37:57

The pipe isometrics sound like a major backward step. I got our design and draughting department to stop doing drawings for pipes that were just a piece of bent tube. As we had a CNC bending machine the best way to designate the pipe was as a set of coordinates. That made the shape independent of the bend radius of the tooling used. We had assembly drawings as a result with up to 40 small pipes made from 1/4", 3/8" and 1/2" tube where there was a couple of views of the assembly with bubble numbers to each part and a couple of pages of coordinate tables. We never had scrap from parts that were bent in a mirror image or were the wrong size because the wrong bend die was used once we did that. As there was no visual guide to the shape in a lot of cases we put in the design standard that inspection was simply if it fitted it was correct. The saving in the number of drawings was an important reason for going ahead with it.

Martin C

Thread: cutting spur gears on a mill
20/09/2021 16:30:24

A single cutter formed like a rack with one tooth can be raised or lowered one or two pitches above and below the centreline of the blank's rotational axis to create DP or Module gears. This will be like having a 5 tooth rack cutter. Rotate the blank one tooth position (0, 1, 2, 3 etc) and repeat until finished. Then if you want less faceted faces you can rotate the blank half a tooth (0.5) and move the cutter to the intermediate positions between the first five followed by rotating the blank to the remaining positions (1.5, 2.5, 3.5 etc.) and repeat until finished. Easy with CNC and an a axis, fiddly but doable without CNC.

You can turn HSS with a ground and polished carbide insert.

This is a test piece left over from one I did for a specific need for a 0.4 module 27 tooth gear where an off the shelf gear was not suitable, the actual part was made from brass.

Single tool gear cutting

Martin C

Edited By Martin Connelly on 20/09/2021 16:32:19

Thread: Screw cutting
20/09/2021 16:00:42

I think from the description of the tool "cutting into the thread ahead" that Bazyle has the problem pinpointed. It is easy for a new operator to assume that the compound slide parallel to the spindle centre line is 0° when it is in fact 90°. You need to move 60.5° away from this parallel to spindle position to be at 29.5°. This means that the compound slide leadscrew is 29.5° away from the cross slide leadscrew. You are probably at 90-29.5 = 60.5° in your setup.

Martin C

Thread: A Couple of Questions about Pipe?
18/09/2021 08:52:22

British Standard Pipe (BSP) has a standard wall thickness, it is the size where the bore most closely matches the nominal size. It also came in lightweight. Both schedule 40 pipe and standard pipe were generally the minimum wall thicknesses to use for threaded pipes. Lower wall thicknesses were used to save weight and cost when they could be welded. For some ANSI standards (eg ANSI B36.10) schedule 40 is sometimes referred to as standard and sometimes the equivalent of schedule 80 is X Strong, there is also XX Strong. Pipe is designated as NPS or NB which are nominal pipe size and nominal bore which lets you know what to expect to some extent but you need tables to know exactly what you are going to get with any of these pipe designations.

The term barrel nipple only seems to apply to a nipple with an unthreaded centre section with a tapered thread either side, the result being a barrel shape to the side view. When there is no unthreaded centre section what you have is called a close taper nipple, you also get parallel nipples.

Martin C

Thread: Back to Imperial
17/09/2021 16:03:29

Fiddling while Rome burns comes to mind. Are they going to redefine the pound as a fraction of a kilogram the same way the USA defines their inch as 25.4mm?

Martin C

Edited By Martin Connelly on 17/09/2021 16:05:38

Thread: cutting spur gears on a mill
17/09/2021 15:59:32

Copy your picture into a CAD program and measure the angle. Not 60°. I've done it but will let you find out what it is for yourself.

Martin C

Jason posted just after I started doing it.

Edited By Martin Connelly on 17/09/2021 16:00:39

16/09/2021 17:59:20

Dave, I have made a single tooth, four cutting edges rack cutter (I know it doesn't make sense put like that) using a ground and polished carbide insert to turn a round piece of HSS. Coupled with a CNC mill with an A axis it is easy to cut gears, just a bit slower than a multi-tooth rack cutter, but since it is CNC you don't need to stand over it. As with a lot of this work more time is spent in the preparation and set-up, the actual machining time is not always the issue. The advantage of the single tooth is that one cutter with the correct pressure angle will do lots of different module or DP gears.

With CNC a lot of productive work is done sitting in a comfortable chair.

Martin C

Thread: Saving the Planet or is it ?
16/09/2021 08:52:09

In a relatively cool climate like the UK for a lot of the year the heat from things on standby contributes towards the heating of the house. It is possible that people are switching central heating on a day or two later because of this slight increase in the background temperature in their houses. This one day delay would swamp a year's use of standby for most UK properties.

One of the examples of not looking at the whole picture before coming out with new restrictions was the limiting of the power of vacuum cleaners. Due to lower power they need to be used longer so the overall effect is probably not what was intended.

Martin C

Thread: Fixture plate ideas
15/09/2021 12:57:08

There are a number of people who supply small tee slot plates (5" x 4" ). Two of these will give flexibility to your setups as you can use one or two and have them together or apart as suits. RDG and Chronos sell them for example. Since they are an attachment you can drill/tap them as suits and add holes for hardened dowels if required without doing something to the mill that can't be undone.

Martin C

Smiley removed

Edited By Martin Connelly on 15/09/2021 12:57:32

Thread: Saving the Planet or is it ?
14/09/2021 13:02:09

The latest silliness I have noted was the idea that there are going to be 2 periods in the day when you will not be allowed to charge an electric vehicle to avoid overloading the grid. One in the morning and one in the afternoon total about 7 hours.

Then when everyone has electrically powered heat pumps will they start dictating that they will also have to be switched off at peak demand times as well?

The other stupid thing is the disparity in the cost of a kWh of gas power and that of electric power. Electricity costs about 10 times as much as gas per kWh so if we have a gas hob and an electric kettle and want to save a bit of money we should ditch the electric kettle and use the gas hob to boil water for tea or coffee because even though it is less efficient and uses more kWh overall and is bad for the environment as a result it is a lot cheaper. The same is true for heat pumps. A heat pump system with a COP in the expected range may use half the kWh of a gas fired system but since the cost is ten times higher per kWh for electricity this means that the heat pump running cost will be 5 times higher than a gas fired boiler. These figures do not encourage people to change to a heat pump system so they will do everything they can to keep a gas fired system until the prices nudge people to go for heat pumps.

Martin C

Thread: cutting spur gears on a mill
13/09/2021 13:02:24

It's a bodge method for a bodge job by a bodger. If that's what they want then there's no point discussing it further.

Martin C

Thread: Making Tapered Castellations in Aluminium
13/09/2021 08:01:32

DiogenesII, the second picture in the first post showing the parts spread out looks to have a couple of wavy washers close to the housing that would fit in the diff and provide a set level of friction. Just a guess, needs confirmation.

Martin C

Thread: Character limitation
12/09/2021 18:19:54

You can only directly enter basic text, no pictures and limited formatting. Pictures need adding to an album then loading into a post with the camera icon. If you look at the size of a Word document file with 3000 characters in it you will find it is a lot more than 3000 bytes. There is a lot of extra saved in a Word file.

Martin C

Thread: Workholding Problem
12/09/2021 12:39:25

Don't know what happened to the original link Advise to turn a thin guide bush adaptor

Martin C

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