Lathe tachometer

[Martin 100Participant @martin100]

The problem with a lot of modern kit is they have a speed adjusting knob that goes from say zero to max rpm with no real attempt made at the factory for calibration and a distinct lack of marking of intermediate values.

Couple of cases in my own workship with a Boxford lathe, with a 4 pole direct from mains motor running at 1400 ish rpm, the plate showing the pulley and backgear arrrangements closely follows the reality at the spindle.

For the Sieg X3 it's a knob a long reach away, only visible if you stand to the right side and towards the rear of the machine that does nothing for the first 20% of its travel and just a low and a high gear selection on the head. One gear apparently gives a top speed of 1000rpm the other 2000rpm, but confusingly with a minimum on both ranges is '100rpm' Work out the logic of that, a gear train that does nothing at one speed input but can also provide a 50% reduction at the top end.

Much of the work on the Boxford other than heavy drilling is performed either at the top 1300rpm or the slow backgeared equivalent that escapes me right now. Insert tooling lets you get away with that

The mill is much more sensitive to rotational speeds and while you can wing it, without a tacho you are just guessing. I'd class it as essential.

[Neil WyattModerator @neilwyatt]

Posted by Martin 100 on 09/01/2018 22:39:26:

The mill is much more sensitive to rotational speeds and while you can wing it, without a tacho you are just guessing. I'd class it as essential.

Just to be mischievous… how do you know the right speed before you select it?

[Brian GParticipant @briang]

Posted by Neil Wyatt on 10/01/2018 09:27:19:

Just to be mischievous… how do you know the right speed before you select it?

In my case by a process of elimination

Brian

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Brian G on 10/01/2018 09:48:10:

Posted by Neil Wyatt on 10/01/2018 09:27:19:

Just to be mischievous… how do you know the right speed before you select it?

In my case by a process of elimination

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Thus, if equipped with a tachometer, one can start the process of data-gathering … and get to understand the characteristics of the machine.

MichaelG.

[Martin 100Participant @martin100]

Posted by Neil Wyatt on 10/01/2018 09:27:19:

Posted by Martin 100 on 09/01/2018 22:39:26:

The mill is much more sensitive to rotational speeds and while you can wing it, without a tacho you are just guessing. I'd class it as essential.

Just to be mischievous… how do you know the right speed before you select it?

Using a very big book from Sandvik with lots of formulae in it , spinning the spindle up and tweaking the pot to somewhere towards the bottom of the recommended range.

I can get the CNC mill working fine with quite acceptable rates of metal removal, surface finish, dimensional accuracy and cutter life. But then it's not me it's the machine.

A lot of my difficulty manual milling stems I think from my height and the lack of it on the X3 with the factory supplied stand, giving a very restricted view of the cutting action compared to turning on a lathe (my brace of Boxfords despite being early 1950's and early 1960's have the chunky 80's era yellow chuck guard affording very good visibility) I can, from sight of the swarf and feel through the handwheels know if the feed and speed is right or not on the lathe I very rarely get that when milling. At least with the tacho on X3 I know I'm somewhere in the right area and can eliminate one variable.

Guess it comes down to experience, I've maybe a couple of magnitudes more turning than milling experience. Decades ago as a engineering trainee I was twirling handles on huge very tired mills with worn leadscrews, sloppy gibs and less than perfect HSS tooling, and despite cutting speed calculations ahead of time the results didn't always match the expectations. Since then I spent many hours being frustrated using a Boxford vertical slide and setups that were not even remotely rigid. The visibility of the cutting action is about as bad as you could ever get. The X3 was a huge improvement, but I'd prefer something at least half as big again with significantly more rigidity. A hefty multiple horsepower motor with a VFD would be useful too. I might have even bought something 'big' from Warco last year if they'd have done the Doncaster show.

[Colin LLoydParticipant @colinlloyd53450]

Ah – so it's not just useful for novices. As an ex-scientist, I always want to observe, measure and record my actions. Not for me the "it feels right" approach – although I am starting to get that with experience. If I can duplicate settings from previous recorded observations – I'm more at home. I'm not denigrating those engineers who "fly by the seat of their pants" – it just isn't how I operate. And with CNC machines – there is little opportunity for a machining by feel approach – nearly everything has to be set up correctly beforehand – and digital appreciation of many of the factors in normal lathe and milling operations feeds directly into CNC operation.

[Neil WyattModerator @neilwyatt]

Posted by Martin 100 on 10/01/2018 11:45:10:

Posted by Neil Wyatt on 10/01/2018 09:27:19:

Posted by Martin 100 on 09/01/2018 22:39:26:

The mill is much more sensitive to rotational speeds and while you can wing it, without a tacho you are just guessing. I'd class it as essential.

Just to be mischievous… how do you know the right speed before you select it?

Using a very big book from Sandvik with lots of formulae in it , spinning the spindle up and tweaking the pot to somewhere towards the bottom of the recommended range.

Fair enough, although I think 'somewhere towards the bottom of the recommended range' suggests that we aren't really at odds

For Colin and Michael G. – even if you find the 'right' speed by experiment, the tacho is just providing repeatability, it's still practical experience that's helping you find it before you put it in your notebook.

There's no right or wrong way, it's what works for the individual. While advice and guidance is invaluable, if an approach works for someone, it works.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 10/01/2018 17:41:33:

For Colin and Michael G. – even if you find the 'right' speed by experiment, the tacho is just providing repeatability, it's still practical experience that's helping you find it before you put it in your notebook.

.

Quote so, Neil … I value both repeatability, and knowledge.

MichaelG.

[Mike PooleParticipant @mikepoole82104]

For HSS tools I use 1000 inches a minute as my base calculation and choose the nearest speed to satisfy that. When you just have a pulley set to select your speeds you need to make a decision that is somewhere near the calculated value. There is no need to get your slide rule or calculator out for this as a bit of rough mental arithmetic will suffice. If the theoretical speeds are unsatisfactory then the problem is likely to not be the speed but tweaking the VFD pot can often improve things and is easy to adjust. Checking your tool setup and machine condition can also effect a cure. If you don't have a tacho then you have no idea where you are and cannot reproduce the setup. Just finding a setup that machines sweetly may be enough for most hobby men and we only have to please ourselves but being able to define a start point and even note a finish point has to be useful. For the sake of £10 and a bit of installation time why not have a tacho?

Mike

[not done it yetParticipant @notdoneityet]

Three pages of tacho or no tacho.

Tachos (and VFDs, are a luxury compared to Grandad’s options.

Grandad did OK with six fixed speeds and maybe a back gear. Perhaps he saved hard for a new fangled myford. Or if well heeled, maybe a Raglan. But even with the variable speed Raglan, a tacho was a later luxury and few were ever fitted.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 11/01/2018 03:20:11:

[ … ] Grandad did OK [ … ] a tacho was a later luxury and few were ever fitted.

.

But Grandad would have needed to pay a disproportionately high price for a tacho !

We have the opportunity to buy rhem cheaply. Such is progress

As Mike Poole wrote, immediately prior to your post:

For the sake of £10 and a bit of installation time why not have a tacho?

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 11/01/2018 05:32:14:

We have the opportunity to buy rhem cheaply.

.

Too late to edit ^^^

That should obviously read : We have the opportunity to buy them cheaply.

MichaelG.

[MuzzerParticipant @muzzer]

Posted by Mike Poole on 10/01/2018 23:45:36:

For HSS tools I use 1000 inches a minute as my base calculation and choose the nearest speed to satisfy that.

Mike

The Machtach allows you to enter the diameter of the work (lathe) or tool (milling machine) and the display will tell you the actual surface speed – pretty handy, no tables or calculators required. Or the rpm if you insist. Nice quick little project if you fancy yourself as an electronics nerd.

Murray

Edited By Muzzer on 11/01/2018 09:49:54

[Brian GParticipant @briang]

I was quite happy as a lad with a selection of fixed speeds – there wasn't much other choice. After a 30-year gap, I realised I was turning much too slowly on my son's mini lathe, and it was likely that I would teach him the same bad habits, so a cheap Chinese tacho was an early addition.

It probably only had a couple of month's use, as neither of us tend to look at it often now we have got the feel for the machine, but it was a useful teaching aid and well worth a tenner (including case) and a few minutes installation. If nothing else, its large red display serves as a reminder that the lathe is still plugged in when the lights are turned out

Brian

[not done it yetParticipant @notdoneityet]

Price does not come into it when deciding whether a necessity or a luxury. If one wants one on a machine not endowed with one, just pay up and fit it. The facts of of pricing now and 50 years ago are irrelevant.

I’ve fitted one to my variable speed spindle (with constant speed motor) on a lathe that was supplied nearly 60 years ago. It was my choice. I will fit one to my mill (will have a VFD as well as six speeds). Again it is my choice.

That word ‘choice’ – not needed but available, therefore a luxury. A handy extra, but not a necessity, therefore a luxury. End of.

[Neil WyattModerator @neilwyatt]

Posted by Michael Gilligan on 11/01/2018 09:45:57:

Posted by Michael Gilligan on 11/01/2018 05:32:14:

We have the opportunity to buy rhem cheaply.

.

Too late to edit ^^^

That should obviously read : We have the opportunity to buy them cheaply.

MichaelG.

I assume it was: We have the opportunity to buy rheum cheaply.

As voided by Inspector Clouseau.

N.

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