Ground angle tool checking device

[Steve WanParticipant @stevewan33894]

Hi folks

Just the other day, I spoilt my 2 day turning job at the last stage of thread
cutting. The thread turned out too sharp and thin walls.

My threading tool was not correctly ground. What’s the best way to check the
ground angle tool beside visually checking with an angle gauge?
55 deg and 60 deg is very close.

Wonder has anyone thought of making a magnifier shadow box that can
cast both the angle template and threading tool on to a screen at
a bigger scale for easy checking for the eyes.

This machine is popular in grinding industries and it cost a bomb!

Any cheaper ways to make one for home workshop? Or simply using a microscope and a light below to project a shadow up?

Steve-S’pore

[Steve WanParticipant @stevewan33894]

Ground angle tool checking device

[Sub MandrelParticipant @submandrel]

I’ve got a £30 USNB microscope. Looking at tools under it is easy and illuminating – it shows how rough a ground edge can be!

 

Neil

[Michael Cox 1Participant @michaelcox1]

Hi Steve,

Rather than making a magnifier shadow box it is much easier to use one of the cheap USB microscopes that are readily available at circa 20-30 USD. These provide magnification of up to 400X and are usually boxed with software to make both linear, circular and angular measurements.

Mike

[Tony Pratt 1Participant @tonypratt1]

Hi Steve, you can pretty darn close with a screwcutting gauge and a bright light behind it. Even with my not so young eyes I think I could get the angle near enough as to make no difference.

Tony

[Terry LaneParticipant @terrylane]

The was a short(ish) series on building an optical comparator published in ME quite a few years ago – the author(s) were, from m, Canadian. I built a somewhat simplified version of it, but it doesn’t see much use.

[Terry LaneParticipant @terrylane]

Got it!

[Les Jones 1Participant @lesjones1]

Hi Steve,

There was a thread about March this year dealing with measuring the angle of a screw cutting tool. Its title was “Suggestions please”. There were many good ideas in that thread. Here is a link to that thread.

Suggestions please

 

Les.

[Steve WanParticipant @stevewan33894]

Hi guys

 

Many thanks for the fruitful info!

Yup! The USB microscope is the best solution but it requires a PC and some setup.

 

I’m thinking a small device, handy to keep and simply plug in and view the tool at some magnification.

 

I googled ‘profile projector’ that’s the commercial device availabe. With this design in mind I think whether I can make a simple version using a graphic enlarger projector which is avaibale in graphic stores. It will work like the over-head projector instead of projecting an image on the screen, it would reflect on a frosted screen. Focusing by moving the lens along a vertical axis.

 

Will do more research here

 

Steve-S’pore

[EddieParticipant @eddie]

Hi

I made myself a threading too sharpner ad in Martin Cleeve’s book.

In fact I made two, Set one for each side of the bit to exactly 60 degrees then it is simply setting the bit in the Jig and sharpen it. it applies to Internal and External bits.

No fuss no Mess. Just sharpen and go.

Eddie

[Ian S CParticipant @iansc]

I’v often thought of getting an old style overhead projecter, I think that would work, not portable though. I wounder about a pocket size slide viewer. I just use one or other of those little thread angle gauges, 55*or 60*, never any trouble. Ian S C

[Clive HartlandParticipant @clivehartland94829]

Steve, I am going to stick my thumb in this one.

You say your thread being cut turned out to be sharp crested and thin threads.

When you need to cut a thread the top of the thread is flat, this is so it does not bind in the female thread at the crest!

Your thread blank size should be less than the thread stated dia. by some 0.05mm.

If you coat the blank with a black felt tip pen then you can see when you are close to the correct thread form you are cutting.

The tolerance for threads is quite large and a small error in angle is not a big problem unless we are talking about 2 or 3 degrees.

Always have a thread nut at hand to gauge when you are close and finally finish the thread by running the thread nut down to clean it up.

If you are working to very close tolerance then use a thread form tool tip. This will give the correct thread form and you can still check for fit as you go.

I can see no real need of any form of threading tool viewer and in 60 years of machining have never used one.

I think your problem is a thread dimension one and best to review what you are doing, vis a vis thread depths and diameter.

No doubt someone will jump in after me and decry what I deduced from your posting.

 

Clive

[Richard ParsonsParticipant @richardparsons61721]

Clive you are right. I normally work to about 0.1-2mm oversize and finish with a chaser, if I have one, or a tap/die. If I have neither I use a thread dressing file it is not so good but it is better than nowt.

These size and profile the thread correctly. I also ‘sharpen’ my threading tools by eye to the thread gauge including the ‘flat’ at the tip. Please remember a sharp oblique angle is the beginning of the crack in the thread.

Hope it helps.

[Tony Pratt 1Participant @tonypratt1]

Hi Clive, I totally agree with all you say and if the blank diameter is even u/size by more than .05mm it won’t have any practical effect. I have also found as I get close to size it is best to run a needle file over the crest to deburr it and then take another cut at the same setting. my tools always have a slight radius on the tip just so the thread root isn’t dead sharp. From practical experience even with proper profile form tools the part really needs to be checked for size with wires or some sort of gauge.

Tony

[Clive HartlandParticipant @clivehartland94829]

To clarify, a lot of machinists that I have observed cut threads at the nominal diameter.

On small diameter threads this can be critical as to get what they think is a good fitting thread is in fact a crest ‘Bound’ thread, In doing this the shoulders of the thread are then cut too deep and the result is as Steve has found a ‘Thin’ thread form.

Maybe my 0.05mm is a bit small and that could be 0.1mm, only experience will tell.

The base thread diameter should be established and a small portion of the job should be machined to that diameter and then the thread cut to reach that diameter on the required threaded part of the job.

This will leave the truncated thread crest that is desired for clearance.

Having spent a lot of time making something and then finding that the last bit, a thread is u/s is annoying.

When you make a stub and it needs to threaded a lot of people cut to the thread diameter and then have trouble forcing a die onto it, a little bit of thought and a small diameter change will make life and cutting the thread a lot easier.

Also, trying to force the die onto the stub or oversize bar will often cause the thread to go wonky!

 

Clive

Edited By Clive Hartland on 31/10/2011 22:24:09

[Ex contributorParticipant @mgnbuk]

Would something like this do :

 

http://www.swissprec.com/CGI/ISPDFF?PMCTLG=01&PMPAGE=96

 

The current J&L offer flyer landed on my desk yesterday – IIRC the basic 7X unit with a standard recticle is under £30, with the extra reticles around £9 each.

 

Nigel B.

[Steve WanParticipant @stevewan33894]

Hi Guys and Clive

Read all your comments and learnt many! Guess I need not make matters more complicated but resolve the root of the problem by grinding the lip angles correctly.

Many of you have done the basic task of grinding the thread cutter with angle gauge for years which have proven not necessary to have a shadow box magnifier.

Will redo my project again.
Thanks!

Steve

[BogstandardParticipant @bogstandard]

Steve,

 

For what we do in our shops, then ‘doing it by eye’ is usually 99.99% good enough.

 

Not everyone has the luxury of a computer in their workshop so that they can use microscopes and things like that, so we usually rely on the old and trusted method of doing things.

 

A thread setting gauge will easily tell you if the angle is anywhere near close, and if it fits snuggly into that, then it will be good enough. BTW, when you check your angles, you will find that 55 degs is nowhere near 60 degs and vice versa, it is very easy to see with your setting gauge.

 

What you MUST ensure is that you use the setting gauge to get the tool tip angles perfectly equal either side of square to the job, otherwise all sorts of weird shaped threads will appear. That is where most single point threading problems occur. In fact when I worked for a living I have seen some metric cut threads that looked like buttress threads, purely because the operator hadn’t set up his tooling correctly.

 

It is all down to getting the basics right.

 

 

John

[Steve WanParticipant @stevewan33894]

Hi John

 

Appreciate your clear guidance and do agree that simple basic checking and grinding will do a good job. When I read your text, it reminded me of my days in technical training what my workshop instructor would say

 

Once again thanks! A great joy to be here to recall the good old days.

 

Steve-S’pore

[Author]

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