modern Digital aids

[adyParticipant @ady]

I’ve used a couple of digital bits to make using my old Drummond easier and I thought I’d share.

 

The first is the obvious one, a vernier on the cross slide.

This is a big asset for an old lathe because it eliminates backlash issues and even allows you to skim a couple of hundredths of a millimeter down a thread which is being cut.

The awkward bit was making the holes in the jaws.

I used carbide tipped masonry drills which were sharpened up on a green grit wheel. HSS will simply bounce off stainless vernier jaws.

So you need carbide to drill these holes.

 

The not so obvious bit is the depth gauge, the thin bit which will poke your eye out if you’re unlucky.

On the cheep verniers these are only heat sealed and can be jiggled out with a bit of patience, I’ve done 3 in a row with no issues. (Photo2)

 

A digital cross slide for a tenner cant be bad.

The ones I have switch themselves off after 60 odd seconds and keep the measurement stored, and use poundland shop AG13 batteries.

 

 

 

Edited By ady on 19/09/2011 11:43:13

[adyParticipant @ady]

[adyParticipant @ady]

The other digital aid isn’t so obvious but might come in useful for a couple of fellow lathe bodgers.

Like everyone else I’ve been watching the screwcutting thread with interest, but in my case I already have a leadscrew clutch.

The problem is I couldn’t previously thread constantly under power, even a 20tpi (20t/50t-8tpi leadscrew) has a double start and needs to be manually reset.

 

My solution was this thing.

http://www.kuebler.com/english2/prod-zlr-vor-ele-901.html

 

It can count backwards, is battery operated and needs a 12v min switch.

 

So by using the tailstock as a backstop and a revolution counter I was not only able to thread a 20tpi but also able to thread metric(10x1mm) constantly under power.

The counter tells you when the correct clutch re-engagement point is coming up.

 

 

Edited By ady on 19/09/2011 11:56:16

[adyParticipant @ady]

A magnet on the back of the chuck triggers the counting switch, so you always know the exact relationship between the carriage/leadscrew(which is up against its rear backstop) and the headstock.

 

For anyone who wants to thread jamjars this also means you can do a multi start thread without ever stopping the lathe.

 

I got lucky with the Kubler 901 because it’s not only battery operated but it counts backwards from a preset number (usually the required tpi) and I found one going cheap, (they are about 100 quid each new).

I’m not very keen on 240v wiring being draped around a working lathe so I wanted battery operated, like those bike computers.

The batteries however are those half size AA lithium ones for photography, 8 quid for two! They are meant to last at least 5 years, which is about how long it takes to get over the shock of buying them.

 

The blue thing is a 12v transformer from a train set for the switch counter, and threading is done with the backgear engaged, it’s too fast under power lol.

 

If nothing else, hopefully I’ve given a couple of folk ideas for themselves.

I think we’re very fortunate to have such easy access to digital bits.

Edited By ady on 19/09/2011 12:24:11

[The Merry MillerParticipant @themerrymiller]

Ady,

 

I thought you were going to talk about digital hearing aids only my wife has just started having trouble with hers!!

 

Len.

[Les Jones 1Participant @lesjones1]

Hi Ady,

I am not totally clear how your system works. When you refer to the clutch do you mean the half nut engagement with the leadscrew or is it a clutch between the leadscrew and the last gear in the gear chain. If it is a clutch is it a dog clutch which only engages in one position per revolution or does it engage at any point ?

 

Les.

[NJHParticipant @njh]

Hi Len

 

Well my wife doesn’t have a hearing aid – digital or otherwise- I have noticed however that she does, at times, have difficulty hearing especially when she finds it convenient! Lets just hope she doesn’t read this or I may experience some ringing in the ears!

 

Regards

 

Norman

[adyParticipant @ady]

If it is a clutch is it a dog clutch which only engages in one position per revolution

 

It’s a single point dog clutch at the end of the leadscrew.

Edited By ady on 19/09/2011 21:00:46

[Les Jones 1Participant @lesjones1]

Hi Ady,

This is my assumption of how your system works. You start off with the carriage in contact with the tailstock the clutch disengaged and the spindle turning. You engage the clutch and note the counter reading when the clutch engages. When you reach the end of the thread the clutch is disengaged either manually or by a trip. You then retract the tool and return the carriage to touch the tailstock by turning the leadscrew by hand. Then move the tool back to take the next cut. Then (With your example of a 20 TPI thread.) watch the counter and when it reads a multiple of 5 counts difference from the starting count re engage the clutch. Is this assumption correct ?

 

Les.

[adyParticipant @ady]

That’s the “principle” both starting points are the same for each pass.

It’s not superfast but it works well.

 

A curious thing tonight.

My main motivation for cutting my own is because stock off the shelf gear can be a bit wobbly and sometimes you want a nice tight “perfect” fit.

 

Tonight I did a 10×1.5mm to fit an off-the-shelf metric nut and eventually got a nice fit where it was too tight for the fingers but a doddle for a spanner and almost zero wobble.

All well and good…except when I measured my own thread the 10mm bar had been deformed at the crests by the thread cutting process to around 10.3 to 10.4mm.

 

So stock nuts can have a pretty amazing amount of headroom built in for the crests which was something I would never have expected nor looked for if I was after a tight fitting thread.

[JonParticipant @jon]

Shame you cant half the cross slide vernier measurement, meaning wind in 1mm its taking 2mm off!

 

[Les Jones 1Participant @lesjones1]

Hi Jon,

I built a remote display using a 16 x 2 line LCD display with this facility some time ago. If you are interested I will find the information for you.

Les.

[Les Jones 1Participant @lesjones1]

Hi Ady,

Does the display count down from the preset number to zero then wraps round to the preset number again or does it then start counting down from 999999 back towards zero ?

Les.

[adyParticipant @ady]

It counts down from the preset, then repeats.

[David LittlewoodParticipant @davidlittlewood51847]

Posted by ady on 19/09/2011 23:56:49:

 

Tonight I did a 10×1.5mm to fit an off-the-shelf metric nut and eventually got a nice fit where it was too tight for the fingers but a doddle for a spanner and almost zero wobble.

All well and good…except when I measured my own thread the 10mm bar had been deformed at the crests by the thread cutting process to around 10.3 to 10.4mm.

 

So stock nuts can have a pretty amazing amount of headroom built in for the crests which was something I would never have expected nor looked for if I was after a tight fitting thread.

 

Ady,

 

This is standard for ISO metric threads – the male thread has a truncated form of exactly nominal diameter (and in practice is often rounded off within this profile) while the female has a root which is rounded and deeper than nominal diameter by at least 0.0504 times the thread pitch. The nut thread crest is likewise truncated (at D – 1.082P) whilst the bolt root is deeper at D – 1.227P. This is done so that there is no risk of interference, even if the tooling is worn. It also has the odd effect that an ISO metric tap actually has a larger diameter than nominal.

 

Your deformed crests are 0.15 – 0.2 mm outside nominal, which may have been within the nut crest or just slightly more then the 0.08 mm gap in the nut root, but if it was more I would guess that, as a thin deformed crest, the excess was easily removed by the force of the spanner. Was it easier to turn by hand after the first tightening?

 

I generally screwcut male threads but (unless using a threading tool of exact profile) run a die down to give final form to the thread.

 

David

[Robin teslarParticipant @robinteslar]

Hi Ady

How is your vernier performing after a year's use?

Do you ever get any trouble with work piece vibration? Of course it shouldnt vibrate, speed or cut is wrong, but sometimes its unavoidable

Cheers

Robin

[Ady1Participant @ady1]

I had a slight leak in the battery, but it cleaned out fine, accuracy is still very good and like backgear it has transformed the use of my hobby lathe

I will now be checking the battery every few months

It's especially useful for screwcutting, eliminating backlash issues and is also good for getting close when roughing down a cut

I haven't had vibration issues but my machine isn't that powerful

Anyway, a job must always be set up to avoid vibration at the start

Very tough jobs get done on the backgear, so no vibration

I can adjust to skim up a thread in a few seconds with no doubts

I alvays shift over to manual vernier measuring once I'm getting close to any stuff which needs to be very accurate

 

Look carefully at my caliper and buy exactly the same model

That particular one:

stores the reading

switches off automatically

can be reset to zero whenever you want

comes on automatically if the cross slide moves

uses poundland batteries

 

If you like what you see you can always buy an expensive full bells and whistles system later on

Edited By Ady1 on 31/10/2012 11:08:15

Edited By Ady1 on 31/10/2012 11:10:44

[Robin teslarParticipant @robinteslar]

Hi Ady

thanx very much for your sound advice, will follow it up and post my experience as it develops

Cheers

Robin

[Cornish JackParticipant @cornishjack]

Ady

Re the Poundland batteries – proceed with caution!! There are AG13s and AG13s! The less good variety will deteriorate very quickly and start to 'salt up' and leak. This is based on a few years part-time watch and clock shop experience where I lost count of the number of watches brought in for repair with corroded battery holders and the watches beyond economical repair because cheap 357/ag13s had been fitted. Similarly, watches which had been left in drawers, unused, with discharged batteries. The 'real deal' batteries are not that expensive nowadays but, at all costs, avoid those packs of multi batteries – just problems waiting to happen!

Rgds

Bill

[Robin teslarParticipant @robinteslar]

Hi Bill

Much appreciated, I am guilty of 99p Shop bargain battery packs. Will have to check some of the gear I used them on

Just bought a Chinese vernier, 6.99 free pnp on Ebay, How real is that!!

I see there are cheaper varieties with plastic jaws, but less accurate 5.99

Blow the expense

Cheers Robin

[Author]

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