Author Topic: It's the little things that catch you !  (Read 10939 times)

Online awemawson

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It's the little things that catch you !
« on: October 25, 2013, 10:56:17 AM »
Today's task was to make an adaptor to mount a large wire wheel brush on the spindle of my buffer. Simple turning and threading exercise. Bore of wire wheel brush 38 mm, diameter of shaft of buffer 19 mm so make a bush clampy screwy thing ! Started by turning down a piece of 60 mm bar to the 38 mm required. Then thread the end an arbitrary thread size for which I need to make a nut.

I decided on 2 mm pitch as I had an internal 2 mm threading insert that fits my boring bar, and had just bought various external threading inserts for the Traub including a 2 mm one. OK set the lathe for 2 mm pitch, and decide how to mount the external 2 mm insert, as I don't have the correct threading holder. Well looking at the insert and comparing with a TNMG insert the overall size is the same. Will it fit?
Andrew Mawson
East Sussex

Online awemawson

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Re: It's the little things that catch you !
« Reply #1 on: October 25, 2013, 10:57:36 AM »
Well they seem to be the same overall shape and fit on the holder
Andrew Mawson
East Sussex

Online awemawson

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Re: It's the little things that catch you !
« Reply #2 on: October 25, 2013, 11:02:35 AM »
So I fit the tool holder to the lathe, carfully adjust centre height, and try to check that there's clearance under the tip (a clue here !)

And off we go threading. total depth of cut for a 2.0 mm thread is 1.2269 mm, so slice by slice we produce what starts off as a nice thread form, but at about 1.1 mm deep oh heck why's that thread so manky? A very careful look at the holder shows it's rubbing the work below the insert despite my having checked earlier, and we are so close to finished depth it's too late to sort things out. Anyway decide to carry on having truncated the tip of the holder to produce an under diameter thread as after all I'm making the nut to suit.
Andrew Mawson
East Sussex

Online awemawson

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Re: It's the little things that catch you !
« Reply #3 on: October 25, 2013, 11:04:53 AM »
Then it dawns on me - the DRO is set up for diameter measurements so is only showing HALF depth of cut - we've a further 1.2269 to go - loads of room to clean up the mess.

So one error, compensated by another error ends up with a workable solution
Andrew Mawson
East Sussex

lordedmond

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Re: It's the little things that catch you !
« Reply #4 on: October 25, 2013, 11:26:11 AM »
don't those threading inserts have a carbide shim under them to set up the helix angle ?

the proper ones that I have do have a shim that need to be changed for different thread pitches

it improper ones from the far east nee chronos RDG do not have the shim

Stuart


Online awemawson

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Re: It's the little things that catch you !
« Reply #5 on: October 25, 2013, 12:47:07 PM »
There should be a shim to give more support to the insert, but I think (may be wrong) that the helix angle is inbuilt to the insert
« Last Edit: October 26, 2013, 04:17:37 AM by awemawson »
Andrew Mawson
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lordedmond

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Re: It's the little things that catch you !
« Reply #6 on: October 25, 2013, 01:14:17 PM »
 I to may be wrong about the actual reason for the shim I only know mine have them


Stuart

just fired up the google fu and found this ( were my threading tools came from

http://www.greenwood-tools.co.uk/ishop/728/shopscr111.html

edited for more info

Online awemawson

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Re: It's the little things that catch you !
« Reply #7 on: October 25, 2013, 01:42:39 PM »
It's an interesting point Stuart that I've previously not looked into. This is what Sandvik have to say:

http://www.sandvik.coromant.com/en-gb/knowledge/threading/thread_turning/insert_clearance_angles/pages/default.aspx

But oddly tool dealers like shop-apt.co.uk where I get my inserts only stock one shim for the whole range

http://www.shop-apt.co.uk/shims-seats/tne16-shim-seat-for-apt-ser-16er-threading-tool.html
« Last Edit: October 26, 2013, 04:18:29 AM by awemawson »
Andrew Mawson
East Sussex

lordedmond

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Re: It's the little things that catch you !
« Reply #8 on: October 25, 2013, 01:56:28 PM »
sandvik tells the same as greenwood but call it flank clearance

as usual its a mine field and it depend where you look for the info i would believe the chip manufacture rather than the dealers

may people with more knowledge than me will chip in

Stuart
 

Offline vtsteam

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Re: It's the little things that catch you !
« Reply #9 on: October 25, 2013, 02:03:23 PM »
I've got less knowledge for sure, and not a dealer, but this kind of came up for me last threading I did -- not with an insert, but a ground HSS tool.

Technically, the clearance angle is variable depending on the pitch and diameter -- the helix angle -- if you want an ideal clearance. But you can also grind in what is an excessive clearance angle, as long as what's left is strong enough to handle the forces and material. Then the tool can be used for a wider range including lesser pitches or wider diameters. It will wear faster however. So maybe that's what the more "universal" inserts do as opposed to those that use wedges, or have a specified low range of helix angle.

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: It's the little things that catch you !
« Reply #10 on: October 25, 2013, 02:30:40 PM »
One other thought. If you have variable shims for an insert you are slightly altering the thread profile. Obviously that must be an acceptably small amount, since they supply them. But it must occur to some degree in that type. The tools that don't use shims can have an ideal profile, but probably overdo the clearance for most threading in their range.

Or do I have that backwards? Is the ideal thread profile normal to the axis of the part, or normal to the helix angle? I assumed it was normal to the axis.
I love it when a Plan B comes together!
Steve
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Online awemawson

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Re: It's the little things that catch you !
« Reply #11 on: October 25, 2013, 05:02:49 PM »
I >think< I've sussed it.

If you look at the chart in the Sandvik link I posted above, the vast majority of threads fall in the 'needing 1 degree' category so the 1 degree supplied shim is right in virtually all 'normal' threads, so  this is why most dealers only supply that shim. Sets of other inclination shims are available at significant cost  but rarely needed.

Andrew
« Last Edit: October 26, 2013, 04:15:49 AM by awemawson »
Andrew Mawson
East Sussex

lordedmond

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Re: It's the little things that catch you !
« Reply #12 on: October 26, 2013, 04:01:42 AM »
I knew you would sort it

just wind ( clockwork motor ) you up and let you run round a bit and bingo up comes the solution  :lol:


I knew what they were for but not the full story

Stuart

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Re: It's the little things that catch you !
« Reply #13 on: October 27, 2013, 08:17:39 AM »
Well it all turned out ok in the end  :ddb:

This morning I finished off the nut
Andrew Mawson
East Sussex

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Re: It's the little things that catch you !
« Reply #14 on: October 27, 2013, 08:21:05 AM »
I decided to continue an experiment started seven years ago and never finished due to my move. I had heard that hot photographic 'fixer' works as a good durable blacking agent, I bought some, tried it on some bits of scrap and then packed it up and moved house!

So digging the rather fly blown bottle out I set up this blacking rig
Andrew Mawson
East Sussex

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Re: It's the little things that catch you !
« Reply #15 on: October 27, 2013, 08:26:18 AM »
I still had some of the original fixer that I'd diluted about 1:3 which had light yellow flocculations in it. Oh well I thought lets do another test with it.

I sand blasted a bit of scrap, and popped it in having warmed the solution to 75 deg C and sure enough a nice black finish. So I carried on and blacked the rest, and wiped them down with Shell Ensis rust proofing oil
Andrew Mawson
East Sussex

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Re: It's the little things that catch you !
« Reply #16 on: October 27, 2013, 08:33:26 AM »
Now it's important to stir the solution, so I had the bits suspended on some iron wire and was jiggling them. The last part to do was the nut, jiggle jiggle,  :bang: CRACK  :bang:

I'd knocked the side out of the beaker - quite a neat hole! A gush of the diluted fixer shot out, over my lab coat and jeans leg onto the floor.

I quick bit of dashing around mopping up then another dash towards the washing machine to strip off and wash the chemicals of. Now you need to understand that our 'laundry' is a building adjacent to the house but not connected - there was I bereft of trousers, and guests due any moment.  :bugeye:

Another quick dash into the house passed undetected fortunately and decency was restored  :lol:
Andrew Mawson
East Sussex

Offline Pete.

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Re: It's the little things that catch you !
« Reply #17 on: October 27, 2013, 08:44:40 AM »
Blimey, it sounds like you were lucky the guests didn't catch you with your little thing out :D

Offline mattinker

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Re: It's the little things that catch you !
« Reply #18 on: October 27, 2013, 08:46:38 AM »
I still had some of the original fixer that I'd diluted about 1:3 which had light yellow flocculations in it. Oh well I thought lets do another test with it.

I sand blasted a bit of scrap, and popped it in having warmed the solution to 75 deg C and sure enough a nice black finish. So I carried on and blacked the rest, and wiped them down with Shell Ensis rust proofing oil

Tell us more about this experiment, it looks interesting. How long did it take and how resistant is it?

Regards, Matthew

Offline Pete.

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Re: It's the little things that catch you !
« Reply #19 on: October 27, 2013, 08:57:08 AM »
I was thinking the same, but no doubt his 7 yr old bottle of fixer contains some 'dangerous chemical' that's banned nowadays. It'll probably turn all your parts pink or some pastel blue or something....

Offline vtsteam

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Re: It's the little things that catch you !
« Reply #20 on: October 27, 2013, 09:01:31 AM »
Talk about blacking parts.....

Andrew, just how did you know in advance to start this topic out in the Ooops section?

As I remember it, fixer was sodium thiosulfate.

You need to make one of those magnetic lab stirrers, Andrew, only suitable for twirling parts around.
I love it when a Plan B comes together!
Steve
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Offline Meldonmech

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Re: It's the little things that catch you !
« Reply #21 on: October 27, 2013, 09:07:08 AM »
         Two interesting posts, have saved the shim info.  I may have some fixing solution in the loft, must give it a whirl. Nice to know I am not the only one who has little accidents, it does seem to make posts more interesting.

                                                                             Cheers  David

Offline AdeV

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Re: It's the little things that catch you !
« Reply #22 on: October 27, 2013, 10:00:26 AM »
So, the moral of the story is - don't try to blacken your nuts, or you'll end up with your trousers down?
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Or: Zhengzhou, China. An even longer way from anywhere...
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Online awemawson

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Re: It's the little things that catch you !
« Reply #23 on: October 27, 2013, 11:21:28 AM »
I can't remember where or how I heard about fixer acting as a blacking agent. Probably a bit of web trawling by me years ago. I don't know if the blacking is a deposit, or if it converts the surface layer of the steel.

I did try a rub with one of those pan cleaning pads and it stood up to that ok - I wasn't going mad at it as I wanted the finish ON!

With that electric hob, and a pyrex beaker that was too small for it I could only get the solution up to 75 deg C and seem to remember it should be almost but not quite boiling. However it works ok at 75 and dangling the part in it blackened within a minute. No doubt the longer it's in the thicker the black is.

The other thing I have no idea about is it rustproofness (if that's a word) which is why after drying thoroughly under an electric hand dryer I rubbed Shell Ensis rust preserving oil  on the parts.

Considering what happened to the beaker I'm glad I hadn't got it up to nearly 100 deg C as that'd be a lot morec energy to dissipate down my jeans  :lol:
Andrew Mawson
East Sussex

Offline vtsteam

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I love it when a Plan B comes together!
Steve
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Online awemawson

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Re: It's the little things that catch you !
« Reply #25 on: October 27, 2013, 11:37:03 AM »
There you go see, wikipedia doesn't know of this HUGELY important use of sodium thiosulphate  :lol:
« Last Edit: October 27, 2013, 11:59:52 AM by vtsteam »
Andrew Mawson
East Sussex

Offline vtsteam

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Re: It's the little things that catch you !
« Reply #26 on: October 27, 2013, 12:04:48 PM »
(oops, hit edit on your post instead of reply -- sorry -- restored).

Well add it then! Wikipedia is yours to update.  :thumbup:

Just thought you'd be interested in:

It's effect on your person.
It is used in food.
The yellow of the old solution is sulfur, after decomposition to sulphite.
Under another entry Thiosulphite it talks about its corrosive effect on stainless steel. Also carbon steel is mentioned
Its use in patinating copper.

I love it when a Plan B comes together!
Steve
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Offline Manxmodder

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Re: It's the little things that catch you !
« Reply #27 on: January 13, 2014, 01:54:21 PM »
I >think< I've sussed it.

If you look at the chart in the Sandvik link I posted above, the vast majority of threads fall in the 'needing 1 degree' category so the 1 degree supplied shim is right in virtually all 'normal' threads, so  this is why most dealers only supply that shim. Sets of other inclination shims are available at significant cost  but rarely needed.

Andrew,
 the shims are primarily for setting the helix angle and as you say it isn't a problem with the standard 1 degree shim until you start cutting coarser pitches with steeper helix angles.

Then you do need to consider fitting one of the optional shims with a corresponding helix angle to suit the thread being cut.

A significant problem can be encountered when cutting a left hand thread running the leadscrew feed from left to right to cut a left hand thread.

 Rather than using a standard shim of +1 degree which is designed for flank clearance on a right hand thread you need to fit a -2 degree shim to compensate for the opposite helix angle now being generated.(The manufacturers seem to classify a minus 1 degree shim as a minus 2 deg so must be classing +1 deg shims as their datum)

A very inexpensive solution to all of this is to simply fit a thin packing shim under one edge of the tool holder and tilt it to give the required helix angle and flank clearance.

Trick that I use: if you ain't sure about the pending result then cut a dummy run in a soft material like acetal rod and look closely at the results before proceeding with the job for real......OZ.
« Last Edit: January 13, 2014, 02:20:10 PM by dsquire »
Helixes aren't always downward spirals,sometimes they're screwed up

Offline rotorhead

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Re: It's the little things that catch you !
« Reply #28 on: January 18, 2014, 01:05:25 AM »
Hi All,

Regarding the left and right threading issue, I had a similar problem cutting a LH Acme 10 tpi thread with a right hand tip and tool, completely shagged the work and tip (including the shim).

So I bought some Internal tips and found a Left hand threading tool for said 16Ex tips, the threading tools I ended up with have shim adjusting screws, to alter the helix angle (Didn't use that feature though).

Anyway the job went fairly well after that, as the pic below will show, the top screw is my incarnation of the original lower one(original is 9/16" Acme 5 tpi x 2start, new one 5/8" Acme 10 tpi x 1start).
Chris
Ulceby, North Lincolnshire.

Offline Manxmodder

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Re: It's the little things that catch you !
« Reply #29 on: February 14, 2014, 01:21:14 PM »
Hi Chris,I meant to ask you where did you purchase the left handed threading tool from or at least could you tell me what brand is it?.......OZ.
Helixes aren't always downward spirals,sometimes they're screwed up