DIY toolpost grinder?

[daxliniere]

Hey gang,
I need to true the jaws of my 3-jaw lathe chuck and have been thinking about building a small toolpost grinder. It doesn't need to be the world's most rigid or highest powered since I'm really just making it to avoid buying a new 3-jaw chuck.

The current plan is to use an ER11 collet holder as the spindle, a pair of needle bearings (8mm ID, 12mm OD, 12mm long), maybe a thrust bearing on each end and an auxiliary boring bar holder or linear bearing block (with linear bearings replaced with needle bearings). I'm unsure of what I'll use to spin it or how I'll couple that motor, but probably a Dremel since it's 36,000 RPM and I own it already.

Anyone got any thoughts on this?

All the best,
Dax.

 

[Erie Fred]

Why not just make a mount on your toolpost for a die grinder ?
Either air powered (simple round body) or an electric one ?

 

[optima21]

here's my small grinding /millling / drilling spindle using a pair of 12v motors for power and changing the motors /belts can be used from 1000 to 20,000 rpm without speed reduction, so increasing the torque at slower speeds.

Small grinding spindle

many years ago I made a small drilling spindle for use on my lathe and have only used it once in the last decade but its a bit bulky for my hobbymat lathe and not fast enough to be used properly to regrind chuck jaws. then I saw this picture of a potts milling attachment...

www.mig-welding.co.uk

and for grinding the chuck jaws I clamped a piece of nylon in them and used a weak loctite to stick the jaws in position,

then knocked the nylon bar out, trued the jaws and then removed the jaws and cleaned the loctite off.

 

[daxliniere]

Hey Optima! I've studied your build - any reason you didn't just make the spindle mount something that could be fitted straight into a turning tool holder?
And for boring it after you welded on the arm? I fear I might be missing some things here.
As far as the nylon+loctite goes, my plan was to preload the chuck jaws with ring that fits into a channel I'll cut into the jaws.

 

[daxliniere]

Why not just make a mount on your toolpost for a die grinder ?
Either air powered (simple round body) or an electric one ?

Because a cheap die grinder won't have tight tolerance bearings, which I would expect to be necessary for a precision toolpost grinder.
I had been thinking of sourcing one of the old-style Dremel flex shafts which has a straight handle. (The current model has a fancy ergonomic moulded grip which would be too difficult to adapt to mounting) I abandoned that idea because A) it was too hard to find and B) the shaft handle looks only about 12mm or so in diameter, which means that the bearings they must have used would be tiny, so probably not that great.

I do also have an air-powered die grinder, but aside from it being as loud as a klaxxon, I can feel axial play in the bearings. (I got it for free in a bulk-load of stuff at a garage sale.)

 

[Erie Fred]

Because a cheap die grinder won't have tight tolerance bearings, which I would expect to be necessary for a precision toolpost grinder.
I had been thinking of sourcing one of the old-style Dremel flex shafts which has a straight handle. (The current model has a fancy ergonomic moulded grip which would be too difficult to adapt to mounting) I abandoned that idea because A) it was too hard to find and B) the shaft handle looks only about 12mm or so in diameter, which means that the bearings they must have used would be tiny, so probably not that great.

Your grinding chuck jaws, not die buttons.
Your lathe is the limiting factor for accuracy here.
Your lathe is not a cylindrical grinder.
Your grinding the jaws because they are hardened, and hard turning would impose too much force on the machine, set-up, and the jaws themselves,
the outcome would not be acceptable.

 

[daxliniere]

Sure, but why introduce more error with a sloppy grinder spindle when I could use an ER11 collet holder into a pair of needle bearings?

 

[Erie Fred]

Sure, but why introduce more error with a sloppy grinder spindle when I could use an ER11 collet holder into a pair of needle bearings?

If you want to build a machine have at it.
Your "sloppy grinder spindle" put some numbers on it ?
Arm waving won't cut it.
No need to get extravagant on this job.

 

[optima21]

Hey Optima! I've studied your build - any reason you didn't just make the spindle mount something that could be fitted straight into a turning tool holder?
And for boring it after you welded on the arm? I fear I might be missing some things here.
As far as the nylon+loctite goes, my plan was to preload the chuck jaws with ring that fits into a channel I'll cut into the jaws.

my thinking was that it would be slightly more rigid if mounted on a cross slide rather than a toolpost, boring after welding is because the welding will introduce distortion due to the application of heat. my reason for the nylon and loctite was I thought the preload would be in the normal position for turning, but for a smaller lathe as long as the chuck jaws are a decent fit in reality its not going to make much difference, and my method didnt require making any additional fittings.

 

[daxliniere]

Thanks for the answers, Optima. It's a great way for me to learn more about about machine tools in general.

 

[Mark Davison]

Why not just hard turn with a carbide tool?.

 

[daxliniere]

You will have an expert jump in shortly, but basically everything I've heard is that carbide takes off too much.

 

[Seadog]

Carbide doesn't like intermittent cuts. Although brazed carbide is a bit more resilient.

 

[Morrisman]

3 jaw chucks are inherently inaccurate, so how accurate are you hoping to get them?
In the distant past I have taken measurement and ground a few thou of individual jaws on the cutter grinder, just to get the 3 jaw back to reasonable concentricity.

 

[daxliniere]

3 jaw chucks are inherently inaccurate, so how accurate are you hoping to get them?
In the distant past I have taken measurement and ground a few thou of individual jaws on the cutter grinder, just to get the 3 jaw back to reasonable concentricity.

More accurate than the ~0.3mm gap of sunlight I see at one end of the jaws when gripping the workpiece.

 

[GraemeVW]

I need to grind the jaws on one of my 3 jaws.
Something along these lines was my plan for loading the jaws in the correct direction

I've heard of it being done with nuts too, but as long as the lumps you clamp on are all the same size, it should be fine.

 

[GraemeVW]

Oh, as for the question, I was going to make a mount for my dremel to do this, or the dremel flesh shaft. But I have another pendant drill and the flex shaft has a chuck rather than a small collet which opens up my options for bits I can hold so I'll probably use that one instead.

Not bothering to make a trying better as I don't really want to be grinding in the lathe very often.

 

[indy4x]

 

[daxliniere]

Not bothering to make a trying better as I don't really want to be grinding in the lathe very often.

Yes, this is how I feel about it, too.

 

[daxliniere]

I need to grind the jaws on one of my 3 jaws.
Something along these lines was my plan for loading the jaws in the correct direction
View attachment 408681

I've heard of it being done with nuts too, but as long as the lumps you clamp on are all the same size, it should be fine.

Yes, that looks like it should do the trick nicely. But you've got those handy pins which could achieve the thing I was talking about!