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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.

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Thread: Eyesight problems
24/02/2012 19:09:34
Posted by Windy on 24/02/2012 18:47:55:

A skilled engineer showed me the other week how to centralise hexagon bar in a 4 jaw self-centring chuck which was so quick and easy to do.

Something I thought you could not do with that type of chuck.

Windy

Easy, just think about a coincident square and hexagon...... wink

Regards,

Andrew

Thread: new lathe ...can someone identify it?
24/02/2012 08:37:34
Posted by Murray Edington on 22/02/2012 22:46:40:

.............

Murray Edington


Good grief, not the Murray Edington, previously of Cambridge? Welcome to the mad house, sorry I meant forum. I had no idea, you sure kept quiet about that diddy second lathe!

Regards,

Andrew

Thread: Slot milling speeds
22/02/2012 11:29:33

Generally recommended cutting speed for low carbon steel with HSS tooling is about 100fpm. For a 1/4" cutter that works out at 1528rpm, so not too far out. Being cautious you may want to reduce that by a third to a half. I think the real problem is the feed rate. If we assume a 2 flute cutter at 1600rpm a feedrate of 40mm/min gives a chip load of about half a thou per tooth. That's pretty small; it's inviting the cutter to rub rather than cut. I suspect that's why the cutters are being blunted.

Why not try a speed of 1000rpm and a feedrate of 80mm/min?

Regards,

Andrew

Thread: New website editor
16/02/2012 23:35:55

Hi Dias,

I don't think you need worry about Neil's comment. I think he's making a play on an unfortunate spelling mistake. I assume you meant to write:

'test' - to try something out

instead you typed:

'teste' - which Neil has converted to the plural 'testes', part of the male reproductive organs, for which a slang equivalent is 'b@ll@ocks'

I don't understand the 'no signal' bit though; and I would claim to be a native English speaker.

Regards,

Andrew

Thread: Problems machining brass - Bad finish !
16/02/2012 16:31:35

Definitely something odd here. If there's noise and vibration it would seem that the lathe/tool combination is not cutting correctly. Have you managed to successfully turn any other metals, ie, is it a generic problem, or just a problem with brass? Are you sure the material is brass? What does the swarf look like? For brass it should be a fine stream of very short chips; the damn stuff gets everywhere! What speeds, feeds and depth of cut are you using?

It must be possible to get to the bottom of this!

Regards,

Andrew

Edited By Andrew Johnston on 16/02/2012 16:32:02

Thread: How to check for parallel?
16/02/2012 10:52:26

In my experience a shaper will easily produce one flat surface, but getting one to produce two parallel surfaces is more of a challenge. The basic cutting geometry of a shaper is against producing parallel surfaces.

For really parallel surfaces use a surface grinder.

Regards,

Andrew

Thread: Problems machining brass - Bad finish !
15/02/2012 20:38:30
I have no problems turning brass using carbide tools. One, I'd be suspicious of the quality of the Machine Mart carbide inserts. Two, I'd drop the speed to 1400rpm, which is still 549fpm, pretty ambitious for a small lathe.
 
Regards,
 
Andrew
Thread: Whistling Cutter
15/02/2012 20:34:31
David: The simple answer is that something (cutter, part, machine) is vibrating at a frequency which happens to be in the audible range. Now as to what causes it; that's more difficult. However, empirically I find that too low a feedrate often causes vibration or squealing, as the cutter is cutting, rubbing, cutting, which excites the cutter and causes it to vibrate.
 
Regards,

Andrew
Thread: How to check for parallel?
15/02/2012 20:29:56
Indeed both sides of a part can be planes. If the planes are a constant distance apart over infinity then the planes are parallel. By definition a plane is flat. If the planes are not a constant distance apart then they are not parallel, although they are both flat. If the surfaces are not planes, but are a constant distance apart, then the surfaces are neither flat nor parallel.
 
To take Nigel's example of two concentric circles; I agree that two points, one on each circle, and on a common radial will be the same distance apart anywhere around the circle. However, they are not parallel. The tangents to the circles at the two points will, however, be parallel.
 
It all boils down to basic Euclidian geometry; which I suspect is a step too far from the OPs original question!
 
Tel: Sadly the earth isn't flat, but is based on spherical geometry, which is a non-Euclidian geometry in the which the 2D surface happens to be a sphere.
 
Regards,
 
Andrew
Thread: Whistling Cutter
15/02/2012 17:14:47
Two things; first while a depth of cut of half the cutter diameter is a good rule of thumb, it is prehaps a little ambitious for gauge plate, assuming a full width cut. Reduce to 2.5mm.
 
Second and possibly more important you must keep a positive feedrate going with gauge plate; at least 1-2 thou per tooth. If you let a HSS cutter rub, even briefly, it's bye-bye cutter. Been there, done that; I now use carbide cutters for gauge plate.
 
One other thought; what surface speed are you cutting at? For oil hardening steels you should be below 50fpm, and probably much lower, say 25fpm?
 
Regards,
 
Andrew

Edited By Andrew Johnston on 15/02/2012 17:15:04

Thread: How to check for parallel?
14/02/2012 22:12:05
Posted by Tony Pratt 1 on 14/02/2012 21:39:17:
......... Please note this wont tell you if your part is straight or bowed.
Tony
 
Agreed, but if the part is bowed then by definition the two sides are not parallel, even if the distance between them is the same. Only straight lines and planes can be parallel.
 
If I wanted to check if a part had parallel sides I'd use a surface plate and a test indicator. If the test indicator does not move as the part is moved around underneath it, for both sides, then the two sides of the part are parallel.
 
Regards,
 
Andrew
Thread: What cutting tools for mini - lathe (HSS or Carbide Tipped ?)
14/02/2012 10:26:34
Posted by KWIL on 14/02/2012 09:32:14:
It is a fallacy that you must use coolant with carbide tipped tools (inserts). Their use is a matter of practice and experience. The specs and other info is available for the model engineer (talk to Greenwood Tools). By the way Colin you can take fine cuts, one of my party pieces is around bar with a 0.0004" step on it
 
Listen to KWIL, he knows what he's talking about. It may also be informative to read this thread:
 
Thread: New "Kid" on the block
13/02/2012 22:25:01
Hi Bob,
 
Welcome to the forum. Everybody has to start somewhere, and no matter at what level one is, there's always something new to learn. Ask away; there are some very knowledgeable people on the forum, and I'm sure you'll get helpful replies.
 
Regards,
 
Andrew
Thread: Automatically 'closing threads' idea
13/02/2012 20:37:15
Personally I disagree. Some build threads are only posted to infrequently, but are nevertheless interesting when posted to, even if they have been dormant for a while. As another example, some months ago I started a thread about the finishes obtaining when turning using insert carbide tooling under a variety of conditions. I intend to add further posts to this thread as and when I get time to experiment with more types of material. I wouldn't be able to do that if it was arbitrarily closed.
 
Regards,
 
Andrew
Thread: Imperial/Metric?
11/02/2012 23:11:57
Posted by Alan Worland on 11/02/2012 20:58:23:

I wonder if we will see the day when machines just have 'handles' with the operator selecting the units as required - sounds quite a good idea!
 
Alan
 
We already do; it's known as CNC.
 
Regards,
 
Andrew
Thread: Is this scrap?
06/02/2012 20:13:40
Posted by chris stephens on 05/02/2012 19:26:59:
"Bin it" BIN IT are you mad....

 
Yes; why on earth would I want to be sane in a crazy world?
 
Andrew
Thread: Mystery Tooling
05/02/2012 20:23:05
Thanks for the further information confirming the use of the items. It's an interesting video posted by JasonB, but also frustrating! I'd rather assumed that the tap was held at right angles to the thread, to stop it rotating; but the video clearly shows this not to be the case. Rather annoyingly it doesn't show how the tap is actually held and what stops it rotating.
 
PMs sent as appropriate for those who expressed an interest in having some of these taps.
 
Regards,
 
Andrew
Thread: Is this scrap?
05/02/2012 16:35:59
Bin it! The saw is pretty fine pitch; that's fine (!) for slotting screw heads, but not much use for anything else. For any decent depth of cut you'll need a much coarser tooth pitch so that the gullet (space between teeth) is bigger so the swarf won't jam the saw.
 
Regards,
 
Andrew
Thread: Mystery Tooling
04/02/2012 16:06:22
Martin & John: Spot on; that's what I think they are, bent shank taps for use on automatic nut tapping machines. The shanks are smaller than the thread core diameter, so the nuts can slide down the shank. What I don't understand is how the nuts fall off the other end, as the tap must be held somehow. I did think of something like the two clamp method, as suggested by John, but it seemed a bit hit 'n' miss. I guess if the fingers were timed correctly you'd avoid clamping one's nuts by mistake? God only knows why I bought them; idle curiosity is all I can think of, but at least it didn't break the bank.

Neil: I'll be happy to send you an assortment FOC. Be aware though that they're rather odd sizes. There's a lot of BA, some UNC/NF, Whitworth and metric and some other oddities. If you can't read the sizes from the picture let me know and I'll PM you a definitive list. Some of the taps are loose in the boxes, but others are in sealed plastic bags with wax over the tap proper, and so are presumably unused.

Regards,

Andrew
Thread: Rina and T&K drawings
04/02/2012 15:43:01
Jason: What with the price of copper these days I'll be straight down the scrapy; while they're still paying cash.
 
Norman: Apparently not; clearly it hasn't affected the ivory towers yet.
 
Regards,
 
Andrew
 
 
 
 
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