MEW-169 Tool-post Grinder Article

[Gone AwayParticipant @goneaway]

Since I’ve never, ever used a tool-post grinder, this may be a dumb question but …

 

In the MEW-169 article on mounting a rotary tool for use as a tool-post grinder, wouldn’t the tool mounted as shown be rotating in the wrong direction? That is the grinding bit surface would be rotating in the same direction as the work surface.

 

Or is that how tool-post grinders are normally used?

[Gone AwayParticipant @goneaway]

[John OlsenParticipant @johnolsen79199]

I haven’t seen the article, but I use an air die grinder in the tool post when occasions arise. I set the lathe turning slowly backwards so that the movements oppose each other. There is no worry about the chuck unscrewing with the low speeds and low cutting forces involved.

 

regards

John

[Steve GarnettParticipant @stevegarnett62550]

The other way around the problem (which works fine with small grinders) is to grind from the rear, which saves you from running backwards. We did this with one job – a small grind on a lot of parts – and the worst problem was trying to keep all that nasty invasive grinding dust off the bed and other critical bits of the lathe. Even setting up a local dust extractor right next to the job didn’t get all of it, and you really do want to – it can do a lot of damage. But this way is better than running backwards – generally the dust gets thrown up in the air (well it did on our job) and it was easier to catch most of it because of that.

 

If you can find alternative ways of doing this sort of job, it’s almost certainly worth it.

[Rob StevensParticipant @robstevens54297]

Possibly a silly comment but I would have thought with the relative speeds involved it would not make a great deal of difference whether the grinder was rotating in the ‘wrong’ direction or not.

 

Also grinding from the front the dust would be directed mostly downwards.

 

However, I’ve absolutely no experience with grinding in the lathe.

 

Regards  all

 

Rob

[Anonymous]

Can’t say I’ve ever used a grinder on my current lathe, as I don’t want to impair the accuracy with grinding paste. However, I do have a cylindrical grinder in the workshop and the work always rotates in the opposite sense to the grinding wheel. The work obviously has to rotate to achieve roundness, but I’m not sure why it should be in the opposite direction.

 

I can think of two reasons. One, grinding is a pretty crude process at the particle level, lots of negative rake. So the relative surface speed has to be high to heat and soften the chip, which aids the shearing process. Given that, it wouldn’t make sense to negate the relative surface speeds obtained by rotating the work and wheel in the same direction. The other reason may be that rotating work and wheel in the same direction is equivalent to ‘climb’ milling, and the grinding wheel particles may not like the sudden increase in load?

 

Regards,

 

Andrew

[David Clark 13Participant @davidclark13]

Hi Sid

The bracket was originally made to grind internally things like chuck jaws or spot holes. This would make the direction correct.

If you want to grind externally you could run the wheel at the back or run the chuck in reverse, ideal to spin pilots down on counterbores.

The slow speed and tiny cut would be very unlikely to undo the chuck.

regards David

 

[BogstandardParticipant @bogstandard]

I was taught to always go with the wheel when using a toolpost grinder, so for external grinding, normal spindle rotation, for internal grinding, reverse the lathe direction.

 

What a lot of poeple don’t realise that when toolpost grinding, you are only removing tenths of a thou at a time. For a normal lathe (without a DRO to allow you to set such small numbers accurately) , you use your compound set at a very shallow angle to give you the small forwards or backwards feeds, then your saddle to give you feed along the job. Normally the cross slide is just too coarse a feed.

 

A normal sort of toolpost grinder usually has two pulley speeds. Fairly slow, say 5 to 6K RPM for external grinding with a wheel around 4″ or less, and a higher speed, say 9 to 10K RPM for internal grinding, where you normally use a mounted point, which can run at much faster speeds.

 

They are rather rare beasts nowadays, so people now tend to make their own with the correct high speed spindles, but motor rotation is the usual problem. I was lucky and was given a broken Boxford ‘Little Giant’, which I re motored.

Many years ago, Chester UK used to sell them , but sadly now they don’t. But if you can get the electrics sorted out, Little Machine Shop sells a nice compact range.

 

 Toolpost grinders

 

 

Bogs

 

[Anonymous]

Of course I’m talking nonsense here; the wheel and work rotate in the same direction so that the relative motion at the wheel/work interface is opposed.

 

Clearly I’m not firing on all cylinders (sorry about the pun) this morning. I need more coffee!

 

Regards,

 

Andrew

[Gone AwayParticipant @goneaway]

Seems I wasn’t totally out-to-lunch with my question anyway.

– I hadn’t considered the internal grinding possibility … although I don’t recall that being mentioned in the article (could be wrong)

– It did occur to me that it could be used at the rear of the part but that would limit it to surfaces close to the end of the part else the mount for the rotary tool would get in the way, at least in the current design. Nor could you use a tailstock centre.

– I had thought that running the chuck in reverse would be problematic on, say, Myfords for example – though mine always seems pretty firmly attached when I have to take it off (yes, I do know how to loosen it). So it’s probably true that for light loads it could be done that way.

– The point about the fineness of the feed seems valid to me. And even setting the top-slide over would, I suppose,  preclude use of a parallel grinding cutter with the design in the magazine. You could, I guess use a rounded cutter or the corner of a parallel cutter but that would not allow you to cut close to a shoulder. Tapered cutter perhaps? Come to think of it, it should be possible to modify the design to crank the tool over to compensate for the top-slide angle too.

Edited By Sid Herbage on 23/10/2010 16:38:46

[BogstandardParticipant @bogstandard]

Sid,

 

You only move the compound to an angle to get your very fine feed, the grinder is set to parallel if you are grinding a parallel job. 

The problem arises when you have to use the compound to grind an angle, then you have to use the cross slide for your feed.

 

When using the compound to do a parallel cut, you dress your stone by the use of the saddle, backwards and forwards. For when dressing to grind an angle, you use the compound to dress the wheel against the diamond.

 

It might sound difficult, but when you get used to using one, it becomes second nature.

 

I hold my dressing diamond in an old mag base. so I can just stick it wherever it is needed.

 

This is internally grinding the nose of a 5C collet chuck when fitting it to my lathe, to remove the runout, it was a cheap collet chuck. Notice the direction of cut, spindle is running clockwise, and the chuck is running slowly in reverse (65 RPM, the slowest my lathe will go). The forwards feed is by use of the compound because it is grinding an angle, and the fine cut is put on with the cross slide 

 

 

 

Dressing the external wheel, this was done with the compound because I was setting up for grinding an external taper.

 

 

 

Grinding up the external taper. Again notice the way the wheel and job are turning. Wheel clockwise, job anti-clockwise, faces running with each other.

 

 

This was fed by hand using the compound, and took about 30 minutes to go fully one way and back. It really needed another lick over to get a better finish, but my hand and arm couldn’t give any more. Toolpost grinding isn’t a quickie job when doing tapers. For parallel long work you can use your saddle feed at it’s lowest, that saves your arms and hands a bit..

 

 

I hope this explains it a little better.

 

 

Bogs

[Gone AwayParticipant @goneaway]

Posted by Bogstandard on 23/10/2010 18:32:30:

You only move the compound to an angle to get your very fine feed, the grinder is set to parallel if you are grinding a parallel job. 

Yes, of course ….  Duh !

[BogstandardParticipant @bogstandard]

Sid,

 

Just to pick up on something you said in your post.

 

Because the loading is so light and you also run your spindle at very slow speed, there isn’t really any chance of you chuck coming unscrewed.

 

I can reach into an internal grind by about 3″ because I have a tiny collet chuck that mounts onto the spindle and by using a small mounted point, I reckon about 1/2″ is the smallest internal that can be ground. But if I don’t need to go more than say 1.25″ deep, I can get a 1/8″ mounted point into it, so the min size would then be about 5/52″.

 

Bogs

[John OlsenParticipant @johnolsen79199]

Couple of points arising:

 

Changing the location so that you are grinding at the back instead of the front does not alter the relative motion of the job and the grinding wheel. If you want the two to be opposing you have to reverse one or the other.  I am not sure how critical this is, but since I can reverse the lathe, this is how I have done it.

 It does alter the direction that grit will be thrown.

(Grinding inside does of course reverse the relative motion.)

 

Second point about grinding on the lathe..yes, we do want to avoid getting grinding grit into unwanted places, but let us not be unrealistic about all this. The atmosphere is full of dust, a large proportion of which is nasty abrasive substances like aluminium oxide and the like. While your lathe is standing still, this stuff is happily sticking to the nicely oiled ways. So OK, we don’t want to make matters worse, but if we take reasonable precautions and clean up well we are not likely to cause ourselves too many problems down the track.

 

regards

John

Edited By John Olsen on 24/10/2010 01:14:56

[BogstandardParticipant @bogstandard]

John,

 

My second picture was set up, just to show what needed to be done. Actually, the dressing stage has to be even more protective than the cutting stage, as the grit flies everywhere.

 

When actually doing the job, because it is such a localised and slow process, what you see in my pictures is actually the protection used. Usually, I used a paper based, but non flammable towel type, and just gathering it up carefully gets rid of all the debris. I mentioned non flammable because I have had cloths set on fire before now by the sparks coming off the job. So have a fire extinguisher handy within easy reach as well.

 

Bogs

[BogstandardParticipant @bogstandard]

A very simple build here by a friend who lives just around the corner from me.

 

Easy toolpost grinder 

[Steve GarnettParticipant @stevegarnett62550]

Posted by John Olsen on 24/10/2010 01:13:33:

Changing the location so that you are grinding at the back instead of the front does not alter the relative motion of the job and the grinding wheel. If you want the two to be opposing you have to reverse one or the other.

 

It was a while ago we did this, and I’m now trying to recall exactly what we did. You can’t reverse the grinder easily without the arbour flying apart, but it’s dead easy to reverse a S&B 1024, so that’s the most likely answer. It’s definitely the grinder that flings the grit about, and that definitely flew upwards when mounted at the rear.

 

As for the need for opposing motion, I’m not sure either how much difference it really makes either, given that so little material is removed and the relative speed difference is so great.

 

As for the dust – well the amount the grinder threw out directly over the lathe compared to what settles on it from the atmosphere – there’s no comparison. You have to catch what you can, and spend quite a while cleaning up the lathe afterwards.

[David Clark 13Participant @davidclark13]

Hi Bogstandard

Can you put me in touch with the grinder maker?

regards david

[BogstandardParticipant @bogstandard]

 Steve,

 

As for the need for opposing motion, I’m not sure either how much
difference it really makes either, given that so little material is
removed and the relative speed difference is so great.

 

As
for the dust – well the amount the grinder threw out directly over the
lathe compared to what settles on it from the atmosphere – there’s no
comparison. You have to catch what you can, and spend quite a while cleaning up the lathe afterwards.

The answer lies in the actions of the two surfaces. If going against each other, not only does your dressed wheel loose its trued up and sharp face much quicker (the crytals get smoothed off), in other circumstances, you will encounter localised surface hardening because of the heat being generated.

In manufacturing they get away with that by flood cooling.

With regards to gathering up dust.

Yes you have to do it, but there is just no reason that some people go to the lengths that they do.

Most wheels are ali oxide that we use, and the reason the wheel is dressed is just not to get it flat, but to break the tips off the bonded granules to give sharp cutting edges again. The loose stuff that comes off the dressing and grinding procedure very quickly gets broken down into nothing more than rounded bits of dust, with no sharp edges at all.

How many grinding machines have you seen falling apart after ten or twenty years use, and that grit gets into everywhere, so are their high precision ways worn out?

I very much doubt it.

 

I stripped down my old (over 50 years) very well used Herbert surface grinder a couple of years ago, and that was caked in this so called ‘murderous compound’ both underneath and around the ways. The hand scraped ways were as good as the day they were fitted together. So I see no reason to believe it will be any worse on my lathe. Lathe beds wear out fairly quickly anyway if they are abused, and that happens to people who don’t use a toolpost grinder.

 

No one worries about the high carbon steels that they chew up, where the chips get red hot then cooled by suds. Now those are as bad as having micro HSS cutting tools all over your machinery. Yet people will work for weeks with that hanging around their machines, or dragging it up and down the ways as swarf. You may as well get a file onto them, a least that would be cutting a little more true.

 

Lots of people get completely paranoid over grinding dust, but will just let normal swarf build up on their ways and let it cut them into worn out chunks of metal.

 

 

Bogs

[Steve GarnettParticipant @stevegarnett62550]

I have an Exe surface grinder that I’ve yet to install in the workshop, and that’s covered in the aforementioned ‘murderous compound’ as well, seemingly mixed up with grease, but as you say there isn’t much on the ways themselves. As much as anything though, that’s because the ways themselves are completely covered during use, so grinding detritus doesn’t fall on them directly – it’s only the ‘atmospheric’ stuff that gets around them. And that’s not quite the same with a lathe, is it?

 

It’s also the case I think, that any lathe with felt pads fitted at the ends of the saddle is more likely to have those collect the dust before it can do any significant damage, so if you are going to use a lathe for grinding to any significant degree it might well be worth retrofitting these if you can. I seem to recall that there was an MEW article about this a while back, wasn’t there?

 

And there’s a pretty fine line between paranoia and common sense sometimes. Common sense dictates that you are aware of what you are dropping on your lathe bed and promptly scraping along the ways – unless of course you are so darn rich that you can afford regrinds every so often. So you aim to keep it clear, don’t you? It’s only the degree to which you do (or don’t do) this that determines how paranoid you are, not the actual doing of it, I’d say!

[JDEngParticipant @jdeng]

My first post on this forum!

 

Just to be clear, the job and the grinding wheel have to rotate in the same direction, ie. both clockwise or both anti-clockwise. This means that at the interface between the job and the wheel both surfaces will be moving in opposite directions.

 

From memory, when I was an apprentice (and it is a good few years ago now!!) I seem to remember being told that it was necessary to rotate in this manner because it ensures that the job is ground truly round. If the job and the wheel are moving in the same direction at the interface (ie. one is going clockwise and the other anti-clockwise) there is a chance that, at certain speed combinations, the job will be ground as a series of flats which is clearly undesirable and rather defeats the point!

 

If as Bogstandard is saying, the wheels is losing its edge too quickly then it may be that the grade or type of grit is the wrong choice. If a wheel is working correctly it should expose fresh cutting edges as it works and stay sharp for a reasonable amount of time. It will of course get loaded and dull over time.

 

Regards,

 

John.

[Steve GarnettParticipant @stevegarnett62550]

Posted by JDEng on 25/10/2010 16:37:12:

My first post on this forum!

 

Welcome to the forum! It’s only slightly daunting sometimes – there appears to be a staggering level of overall experience here, one way or another…

 

 

From memory, when I was an apprentice (and it is a good few years ago now!!) I seem to remember being told that it was necessary to rotate in this manner because it ensures that the job is ground truly round. If the job and the wheel are moving in the same direction at the interface (ie. one is going clockwise and the other anti-clockwise) there is a chance that, at certain speed combinations, the job will be ground as a series of flats which is clearly undesirable and rather defeats the point!

 

 Intuitively, this seems to make sense – thank you for clarifying that.

[BogstandardParticipant @bogstandard]

John,

 

Due to forcing you to publish your first post, I thought I had better check on the information that I was told to use and have been using for more years than I care to remember.

 

I have to admit that the information I have been giving people has been incorrect, and for that I apologise.

I don’t know why I have never had any trouble ever since I started to use a toolpost grinder both on my apprenticeship and in my shop, but whenever I tried to go opposite from the way I do it, I never get good results, and it isn’t because of wheel choice.

I suppose the chap who taught me has long since been pushing up daisies, so I can’t correct him, so the blame falls onto myself for pushing duff information.

 

But on the other hand, I have had the information I gave verified many times by professional grinders when I have posted it before. So where do I stand now?

 

No one in this world is perfect, and I am the first to admit it whenever I am wrong.

 

Just to show the info I found.

 

Steve,

 

Your comment about common sense was exactly the thing I was on about.

There is no need to get paranoid over anything, and as you said, it is all down to common sense.

 

Unfortunately there are such people who totally lack it, and so say that you should never do grinding on a lathe because of blah, blah, blah.

 

Why should a very useful technique not be used because a few paranoid people are scaring new starters away from it, before they have a chance to try it for themselves.

 

If I am proved wrong and my lathe gives up the ghost in forty years rather than fifty, I for one won’t be complaining, but if you want to complain about me after that amount of time, send me a message thru a medium.

 

I am a machine user, not a machine polisher, as it seems a lot of these paranoid people are. They are scared to death of scratching the paintwork.

 

 

Bogs

[JDEngParticipant @jdeng]

Thanks for the welcome Steve!

 

After I had made my post I had a look through various textbooks which I’ve gathered over the years and they all state that the work and the wheel should be moving in opposite directions at the point of contact but none of them actually give the reason why. Thus they both need to revolve in the same direction if external grinding and in opposite directions if internal grinding.

 

What they do all agree on is that when toolpost grinding you need to achieve the maximum amount of rigidity in the set up if you are to achieve anything like a decent finish.

 

I’m with you Bogs on using a machine; I think you need to take common sense precautions such as covering slideways, cleaning down well after wheel-dressing and at the end of the job etc but at the end of the day they are machine tools for using. I’ve seen some awful abuse of machinery in industry and it still keeps working – not that I’m condoning that but I do think you’ve got to keep a balance between practicality and keeping something in cotton wool.

 

By the way has anyone seen the new toolpost grinder by Hemingway Kits?

 

John.

[Steve GarnettParticipant @stevegarnett62550]

 

Posted by JDEng on 26/10/2010 08:39:15:

 

I’ve seen some awful abuse of machinery in industry and it still keeps working – not that I’m condoning that but I do think you’ve got to keep a balance between practicality and keeping something in cotton wool.

 

 

I think that to a degree, attitudes vary, and quite rightly so; if you own it, you tend to look after it better – that’s inevitable. And I strongly suspect that if you painted or repainted it yourself as well, you tend to look after it better still. That invariably puts industrial machinery that’s still in industry at the bottom of the heap, and I suppose that it’s an additional justification for most of it being built like the proverbial brick outhouse compared to the Chinese stuff, which generally isn’t.

 

Unfortunately for me, this doesn’t work at all at work. If it breaks, it’s muggins that has to fix it…

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