# Compound Rest mounted grinders



## Brian Rupnow (Nov 9, 2010)

I am curious about this subject. For all intents and purposes, grinding in the lathe is a bad thing, because of the highly abrasive grit created. but---Sometimes it would be so nice to be able to do some really fine finish work with a grinding wheel. Obviously, what I show in the picture is crude, nasty, and ugly. However, as in all things, it has some promise. I'm sure that with a little creative designing I could come up with a method which would include removing the toolpost, (one bolt in my case) and mounting an aluminum adapter block to the top of the compound rest. The only really important thing would be keeping the height of the grinder spindle at the same height as the center of the lathe chuck. By mounting it on the compound rest, I would have the same linear and rotational adjustability and range of movement as the lathe tool currently has. I am not about to run out and buy any type of "retrofit" lathe grinding equipment, but I have nothing against working with what I already have. Of course, whats got me thinking about this is the fact that I would like to reface the valves for my Kerzel engine build. Seems like a grinder with a fine stone would be just the cats meow, so much better a finish than I could ever achieve with n HSS tool. Thoughts, please------Brian


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## cl350rr (Nov 9, 2010)

a possible refinement would be a flex shaft extension of the grinder. construct a stepped aluminum block that could be clamped in your turret tool post, bore a hole through it the size of the hand piece of the flex shaft, split to outside and install a couple of clamping screws and your grinder could be hung above the lathe (out of the chips and grit). the grinder could be rotated to any position that your tool post would adjust to. just a thought


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## kcmillin (Nov 9, 2010)

I have tried this same thing in the past. I had trouble with the grinding stones wearing away quickly. I did not even get one to work. (They were the kind that come in the dremel  grinding/polishing kit. One of them was green in color, and the other was orange-ish.) 

I am also interested in what the more experienced member have to say. I am sure there is a "Correct" stone to use.

Kel


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## Blogwitch (Nov 9, 2010)

A few things to consider.

On a real toolpost grinder, they go to great lengths to have a preloaded and true running spindle. Dremels etc, are no match for that. So don't expect the same sorts of results.

When toolpost grinding, you should only be removing tenths (0.0001") at a time, NOT thous (0.001"), so really, if you are feeding along the length with the saddle, you should be using the compound set at a shallow angle to give you the very fine forwards feed required. If you are feeding with the compound, say to grind an angle, you really need some sort of fine measuring on your cross slide (DRO or dial) to make sure you are feeding in only a tiny amount.

Myself, who has been toolpost grinding nearly all my working life at one time or another can get it wrong. I was informed by my instructor many many years ago that you should always grind with the direction of the wheel, so that is what I have always followed. Now having found some info on the web while casually surfing, I find he was wrong, and so of course, was I. You should always grind AGAINST the wheel rotation.






So really, to do external grinding, you need chuck reversal on your lathe. Don't worry, your chuck shouldn't come unscrewed as you should only be running the chuck slowly and the pressures involved are minuscule.

To plug up every orifice and cover up your lathe in dust sheets while grinding is really poppycock, as long as you don't get your slideways piled high with grinding dust and be doing it every day for years, you should have no worries. When turning red hot chips, you are making immeasurably worse items than grinding dust, and you don't cover up for that. Just a paper towel draped across the bedways, and a good wipe down afterwards should suffice.

Grindstones and mounted points come in all shapes, sizes and colours nowadays, so unless you know exactly what type of wheel or stone you have, it can be difficult to know exactly what to use. All I can say in that situation, if you are not getting good results, try a different stone. Also remember, larger stones require lower revs, True grinders don't run as fast as your Dremels etc, so you might be risking overspeeding your stone and having it blow apart as the bond gives way. Always prepare your safety precautions for that liability, a bit of stone is just as fast as a bullet under certain conditions, and can penetrate flesh just as far.

Whatever you are using, it MUST have the cutting face dressed up before use. Not only to get it running true, but to break off the surface granules of the stone and leave nice sharp edges for it to work correctly. If you have your grinding speeds correct, the stone should semi dress itself during use by discarding worn granules out of the bond and leaving sharp edges behind. If it starts to burn the face, things are not set up correctly.

These points I raised above are just a few bits of basic stuff to attempt to help you understand what you are getting into. It could go on forever.

What you must realise, grinding is a specialist trade, and it can take years to master. I am not a skilled grinder, far from it, but I have been on numerous specialist grinding courses required by my trade, and have done it most of my working life, and still I make mistakes, and can only skim the surface with the knowledge I have picked up, and here are you gents, coming along and expecting to do perfect grinding in a couple of hours.

I am not trying to put you off trying it out, but you must respect your limitations from the word go. Just because you get a couple of good finishes doesn't turn you into an expert overnight.

Read up as much as you can on the subject, and understand what you are reading, and just maybe, you might be able to get some sort of decent finish on your project.


Bogs


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## Lakc (Nov 10, 2010)

I have tried and definitely failed with my old worn out Dremel, and my new no-brand tool that replaced it does not look a heck of a lot better. 
Like some folks build cam grinders, I have always thought a small dedicated valve grinder would be an easier project. I suppose a Quorn or other toolbit sharpener could be utilized in some fashion.
Preloaded taper bearings and a grinding wheel shaft inside a toolpost mountable bearing housing would have a bunch more utility, providing you could belt/gear/flexshaft drive power to it.


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## mu38&Bg# (Nov 10, 2010)

I rather like this concept. I'd make it with an angular contact pair int he nose. Another tool on the list.

http://www.homemodelenginemachinist.com/index.php?topic=6844.0

I do currently have an old Precise grinding spindle which I've used on my lathe. The bearings need replacement so it's useless for say grinding a crank journal or cylinder. It does work for removing material from hardened steel. I'm looking at replacing the bearings, but need to make a tool to disassemble it.

The quality of finish with a Dremel type tool is going to be limited. I think that for a valve face, it won't be better than a good brazed carbide bit could make it. My Dremel vibrates so much that I wouldn't even consider it.

Here's an old thread on the topic. http://www.homemodelenginemachinist.com/index.php?topic=7659.0


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## krv3000 (Nov 11, 2010)

hi ther is a tool avalebel on ebay to hold a dremel in a tool post see pic


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## narrowgauger (Nov 11, 2010)

Hi Guys

using a Dremel as a toolpost grinder would be an absolute waste of time when taking into consideration that the use of toolpost grinding is to achieve precision finishes and tolerances. Even as a basic hand tool a Dremel is a rather crude instrument.

for precision work you need precision tools.

I have recently built a precision toolpost grinder at very low costs based on a 8mm ER11 spindle from CTC Tools Hong Kong ($A12.50) plus a surplus precision motor ( 8 500 rpm) from a US seller ($US 18.30). This machine can use the full range of ER11 collets to enable a range of grinding wheels as well as other cutting tools to be held with good precision.

for full details of the construction of the unit (total cost $A80.00) go to www.metallmodellbau.de click on universalspindle in the column of projects. you will also find a complete CAD drawing for the construction on this chaps site. whilst you are there also have a look at all the other wonderful special machine tools that this machinist has created.

if you do not want to go to the trouble of building this toolpost grinder at least do yourself a favour and buy a Proxxon handheld rotary tool plus their toolpost clamp accessory. at least you will then have a tool designed for the job and a tool with precision bearings et.

Have fun
Bernard


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## Dunc (Nov 17, 2010)

Wondering if a die grinder, for eg. 
http://www.dewalt.com/tools/metalworking-grinders-die-grinders-dw887.aspx would offer suitable bearing runout? I would guess that it would be better than a Dremel based on above comments but would it be good enough?


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## shred (Nov 17, 2010)

FWIW, a complete Taig headstock is only about $120, though you'd have to sort the motors and pulleys yourself. Should be good to 15K RPM at least.


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## Blogwitch (Nov 17, 2010)

Dunc,

For internal grinding, and if you have piped air (large quantities of it) then a die grinder would most probably be fine. 

The problem with that solution is when using it for external grinding. You use a much larger wheel, and so the wheel would be liable to burst at the speeds a die grinder normally runs at.

To control the air to reduce the speed means that you will have a very low power level available, and would be liable to stall, as die grinder turbines only operate and produce their power by having a fast speed generated by lots of air. 
There are electric die grinders, and some are even variable speed, but their cost is very prohibative compared to the correct toolpost grinders sold by the likes of LMS.

I suppose you could get the speed down by putting a reduction belt onto another spindle, but then you are into the realms of a normal toolpost grinder, so defeating the object of the exercise.

Dremels and the like are like using toys to get the job done, and even then only maybe, compared to a properly made or purchased toolpost grinder.

BTW, I knocked up this rough and ready spindle many years ago to do a specific drilling job on the lathe, and it had a preloaded spindle. It only took a couple of hours, so I am sure that almost anyone could make something similar, but a little better looking, for very low cost and very little time. As far as I can remember, it was controlled for speed by one of the little units for Dremel type drills.


Bogs


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## Ken I (Nov 23, 2010)

Industrial quality grinding spindles and associated workhead spindles are highly specialised.

They are built to run with zero clearance.

This is achieved by using pre-loaded bearings and in many cases tilting pad Mitchell type bearings (Cincinatti - Filmatic) or Trilobe designs (Jones & Shipman) where the lubricating oil is forced into 3 or 5 wedges which allows the spindle to run dynamically with zero clearance.

Even the slightest clearance leads to surface finish problems.

Tools like a Dremel although excellent for purpose are useless as a toolpost grinder.

A homemade well thought out spindle is probably the way to go. This won't get you past clearances in your lathe spindle that you have never noticed before - but on the small work we modelists do you will probably get away with it.

Precision requires precision there's no way around it.

I used to run a line of 60 H.P. #3 Cincinatti's driving a half ton grinding wheel at 100mph (45m/sec) these spindles had 5 tilting shoes at either end. These were production grinding shockabsorber rods.

FYI

Ken


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## SBWHART (Nov 23, 2010)

Hi 

I made my own Tool Post Grinder, Works fine for me.

Build log her http://madmodder.net/index.php?topic=1903.0

Stew


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