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Member postings for Andrew Johnston

Here is a list of all the postings Andrew Johnston has made in our forums. Click on a thread name to jump to the thread.

Thread: Face Mill for lathe
18/01/2020 11:00:23
Posted by SillyOldDuffer on 17/01/2020 17:47:40:

I'm not sure it does, rather metal is sheared off in front of the point, and - maybe - the tool smooths the finish by polishing the rough surface left behind:


The picture illustrates 'Built Up Edge' causing rings on the the work. Could this be what's causing Andrew Johnston's recent woe in EN1A?

Absolutely, the cutting process is shearing, not slicing. I think the tool bit may well burnish the material as it passes, particularly for insert tooling. That may explain why insert tooling sometimes works better at higher speeds. The shear zone is much hotter at higher speeds, so the material is softer and more easily burnished.

Interesting idea about BUE on my EN1A. But I'm not convinced. The tool on the hydraulic copy unit is actually upside down. During roughing the swarf fell away in a steady stream of small blue chips. When finishing the swarf had more of a tendency to produce strings, but again no evidence of BUE. This morning I've used the same holder and insert in the normal toolpost to clean up a nut I welded on to my M16 drawbar yesterday. The insert looks clean and in remarkably good shape given the duty of producing a bucket load of swarf. I've also just cleaned the lathe and it really was a bucket full of swarf!


Thread: Cutting teeth on a spur gear
18/01/2020 10:41:03

There are two different issues regarding undercutting. One, is when is an undercut needed to clear the apex of the mating tooth? Two, at what point will a hob form an undercut, whether you need it or not? The need for an undercut decreases with increasing pressure angle. The need for it can also be removed by increasing the diameter of the smaller gear (same number of teeth) or altering the tooth shape. It sure ain't simple!

I've cut 12 tooth 20PA gears with an involute cutter and they seem to mesh fine. On the other hand 10 tooth 20PA bevel gears machined on a 4-axis CNC mill have an undercut, and need it to mesh without interference.


Thread: Normalizing cold rolled bright mild steel
17/01/2020 19:24:34
Posted by Nigel McBurney 1 on 17/01/2020 17:51:05:
I can never understand why anyone even considers black hot rolled steel ,,thats for fabricators and blacksmiths.

Cost, availability, less prone to rust and machining time.

It's boring enough hogging connecting or eccentric rods out of rectangular sections, let alone round. Bright round is stressed, but if material is removed symmetricallty, ie, turned, no distortion results. Milling it is a different story.


Thread: Lathes as bling!
17/01/2020 14:39:31

Myford - pah. Chinese - pah. Handwheels? Who needs 'em. Be different:

photo1 britan lathe with bar feeder me.jpg


Addendum: I do have a Myford, but it ain't a lathe.

Thread: VFD Question
17/01/2020 13:14:34
Posted by Steviegtr on 16/01/2020 22:49:14:

The windings in most multi speed motors have multiple windings around a pole. So 4 windings on single speed & 8 windings on 2 speed & so on. This does not mean the motor goes from a 4 pole motor to a 8 pole motor as some have suggested. Its just a different winding on the same pole.

I don't follow that? The equation for the synchronous speed (in rpm) of an induction motor is 2 times frequency (Hz) times 60, all divided by the number of poles. Assuming that the frequency is fixed then the only way to change the speed is to change the number of poles. Of course windings aren't added or removed, simply connected in a different sequence. But the upshot is to change the number of poles.


Edit: Thought better of it

Edited By Andrew Johnston on 17/01/2020 13:18:13

Thread: What Did You Do Today 2020
17/01/2020 11:30:34

I did indeed use the former former, with one modification. I've increased the radius on the edge to about 3/32". Here's a close up of the former:

former - modified.jpg

The flange is designed to be 3/4" high. I originally allowed an inch bending allowance. This was far too much. For the plate shown I allowed 7/8" on the straight edges and down to 3/4" on the corners. The height of the corners still grew to more than an inch. So I plan to cut the allowances down a bit more on the corners. This is especially so for the front plate where the corner radius is 3/4" rather than the 1" for the spectacle plate. I intend to reduce the corner allowance to 5/8", ie, undersize. It's like school uniforms, we hope it'll grow into it.


16/01/2020 22:43:43

Third time lucky I've managed to hot form a spectacle plate from 3mm sheet that is acceptable. Here's the plate after forming and cleaning up, with holes drilled in the sides and the bottom shaped with a hacksaw and files:

spectacle plate rear.jpg

And the plate in place with previously made BSF nuts and bolts:

spectacle plate bolted.jpg

Pleasingly the spectacle plate was a nice push fit between the hornplates right off the former. No machining or filing needed, so I must have got the sums about right. The outside of the flanges are a bit pitted where I finished off with the copper mallet to ensure a good fit on the former. I hope that a whizz over with U-Pol will fix that. smile


Thread: Musings on taps
16/01/2020 22:28:31

A. Never really noticed that

B. If needs be I do the same, but I rarely use plug taps, taper is fine for through holes. I use spiral flute taps a lot, you only need to buy one tap, not a set

C. No idea, never used serial taps for V-threads

D. C C. Serial taps can be useful for square and Acme threads. Here's a home made set for a square thread:


E. Never noticed it, but I use commercial tapping heads on the vertical mill and repetition lathe along with spiral flute taps, so reverse just happens. Depending upon tap size I'll run at 500 to 1000rpm

F. Not noticed it with professional taps, although I'm not convinced of size of some of the ME taps I've bought

G. The relief is fairly simple, it's how they get the thread form impressed into the grinding wheel that amazes me


Thread: why does my makita go pop occasionally ?
16/01/2020 16:10:33
Posted by Maurice Taylor on 16/01/2020 15:28:42:

I wouldn’t worry about interference............

Depends upon the type of motor. A brushed DC motor is quite likely to be way noisier than a switch-mode PSU on a PCB.

Was the trip over-current or earth leakage?

Electrolytic capacitors are reknowned for swelling before failure. But I've not seen the same with other types of capacitor. Normally one would expect to see an X-rated capacitor across the supply and Y-rated capacitors from live and neutral to earth. If the equipment is double-insulated then there is no earth and no need for the Y capacitors. Both X and Y capacitors are metallised film and are self-healing as a short circuit failure is unacceptable. If the film is punctured the local metal film is designed to evaporate, removing the short circuit.

A picture would help identify the components, and possibly the problem.


Thread: Drilling holes using pillar drill - work wobbling
16/01/2020 12:58:14

Now you''ve got a man sized drilling machine just drill 8mm and be done with it.


Thread: Hobbymat MD65 - help figuring out accessories (photos)
15/01/2020 10:52:09

Any industrial tool stockist should have, or be able to get, keys for Jacobs chucks. Here's a link to the manufacturers technical page:


The stockists they list are in the US, but plenty of UK stockists for chucks and keys. I'd be suprised if the same wasn't true for Europe.


Thread: rolling brass strip in the lathe
15/01/2020 09:21:53
Posted by Clive Brown 1 on 15/01/2020 08:54:38:

GHT addressed this issue with his design in ME using pinch rollers. This much reduced this effect.

You get the same flat, but only on one end. So the work needs to be swapped end for end on each pass.


Thread: VFD Question
14/01/2020 20:11:05

Mark: Thanks for the explanation.

Gerald: It should run fine in star. If you look at your diagram in high speed mode wires 4, 5 and 6 are connected together, but they don't go anywhere. You don't need a neutral line to run a motor in star. In theory the current in a neutral wire would be zero.


Thread: Face Mill for lathe
14/01/2020 20:00:23

Good grief, that's going to be flexible. I don't think you need worry about spindle loads, any sort of cut and you may well get more chatter than an Islington luvvie. And there was me worrying about whether a 50mm face mill would be too big for a Bridgeport.


Thread: Bottled Gas Suppliers
14/01/2020 15:31:54

Thanks for the additional information. I read somewhere that oxy-propane isn't great for brazing, but can't remember where. Superficially one would have thought it would be fine, as the temperature is much lower than needed for welding.

Much to my surprise the Air Liquide lorry turned up at lunchtime with my refill bottles. Unfortunately I was so surprised I injured myself falling off the chair! Naturally the delivery was a foul up. One, the delivery price was not what I thought I was paying and two, he seemed surprised that there were two bottles to collect. He was pleasant though. Said he'd delivered to me before. Quite possible as when I bought my DC/AC TIG welder I had the argon bottle delivered, as it is too large and heavy for me to lift. But that must have been 10 years ago. He also said I'd be better off with Albee bottles as I'd own them and there's no delivery charge. I mentioned the regulations and the fact that I'm a hobbyist and he agreed I am exempt, but said it was company policy not to allow pickup. He related a story of someone turning up at the shop with a trailer full of propane and acetylene bottles all rolling around in the bottom of the trailer. It's idiots like that causing the blanket ban on collection.


Thread: VFD Question
14/01/2020 15:15:30
Posted by john fletcher 1 on 14/01/2020 14:16:07:
........with POLE changing switching to give the two speeds,and NOT Star/ Delta.

Clearly the switch is changing the number of poles. But if that's all it's doing why aren't the low/high powers also in the ratio 2:1?


14/01/2020 14:11:52
Posted by Gerard O'Toole on 14/01/2020 13:06:17:

My motor, which is the original motor fitted, is marked Siemans-Shuckert , 380V, 2.7/2.8 A, 0.8/1.1kW, cos ó 0.64/0.8, 700/1420 U/min

There is a switch to switch it from low speed to high speed. This switches it from Star to delta ( or Delta to Star - I will have to check)

It may be switching from star to delta, but is also pole switching from 4 to 8. The key is the last part of the plate:

700/1420 U/min

In other words 700 and 1420 rpm in low and high speed respectively.


Thread: Bending brass
14/01/2020 13:58:43

I expect the original was cast. The angles look far too tight for the thickness of material to be bends, and the thickness of the material seems to vary a lot.


Thread: PM Notification Issue
13/01/2020 16:20:10

Not my end; my operating system is no longer supported. So definitely no updates I didn't know about. I'm normally logged out, and only login when I want to make a post or read a PM. I don't have a 'spam' folder. Thanks for looking anyway.


13/01/2020 14:44:01

For ages I've been getting an email to say I have a PM. In the last few days the emails seem to have stopped, even though I have PMs waiting. I've checked that I still have the notification box checked. Also unchecked, saved, checked and saved again. It still doesn't work. What gives? Smacks of an IT 'upgrade' to me!


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