Waldown tool post grinder 

Page 2

What it can do

I've cut and machine long HSS reamers into cutters, refaced milling bits and drills, refaced engine valves, reduced hardened pins, fine finished fly cut surfaces and shafts - just an example of what is possible.

The 35 and 60 degree gear cutters below were machined from scrap end mills, as seen on the left, using a friction disc for profiling.



It can machine small diameter and unsupported work without putting normal cutting loads on them - see the 4 mm HSS Woodroofe cutter and small hardened bolt below.

keyway cutter

Below is a video of the Waldown in action, grinding a badly worn and tapered drill bit to a uniform diameter.




The reduced shank was also badly bent.  Straightening it was not a practical option, so I reworked it.

Seen below cutting off most of the unwanted damaged shank with a disc, and then doing a first pass by hand to remove most of the runout before going on to fine finish it.




You can't do this job any other way.

Here's a tricky job I easily did when restoring my 1930's Schaublin 102 tool maker's lathe.




Improvements to the finish


It is important to lock down the carriage and/or cross slide where possible to reduce the chance of harmonics or backlash affecting the finish.

As grinders put very light loadings on the work piece, any slop in the cross slide will greatly affect the finish as the grinding disc can float in or out if left unchecked.

The simple cross slide lock (red arrow) below will prevent this.  

cross slide lock

It applies additional force against the existing gib strip as required.

See the following video for details on how to fit one.



The lock can also be used to apply pressure/resistance to dampen the cross slide when doing jobs such as shown in the above videos.

You must also dress the grindstone to get a uniform cut and the best finish.

Dress the grind stone

You MUST do this to get a fine and uniform finish.

To dress grind stones I use the simple setup below - a cheap one carot diamond single point facing tip mounted in a plain cross shaft, held between centres with the lathe OFF.

dress grind stone

Mount the shaft in a chuck at each end, set the facing tip angle at 10 degrees below centre and away from the direction of rotation, wind in the tailstock to lock the morse taper on the tailstock,
set the diamond tip cutting depth with the cross slide, then lock the cross slide.

Now fire up
the grinder and use the carriage handwheel to move the diamond tip across the stone surface slowly.

Quick, easy, and 100% accurate.

A 30 degree side angle on the dresser will supposedly keep the tip sharp.  Rotate the tip occasionally to spread the wear.

You can also mount the single point diamond in the chuck to do bevel angle and end faces.

Use rags to cover the lathe and catch the fine dust that results from this exercise.

The perfect finish on the stone below took seconds to do.

dressing a grind stone

This very fine grain stone will give a mirror finish.

Grind stones

Better quality wide stones do a better job.

But I also do a lot of grinding with thin friction discs.  These don't overload the grinder motor, can grind into right angle corners and tight situations, cut off shafts regardless of hardness, are long lasting when used with light loadings, and can give a reasonable finish when used with a very fine feed rate (about 0.6 mm/rev).

Not up to the standard of a wider fine grain stone, but handy for preparation etc.

They are also cheap and  readily available.

The best value and performance thin cutting discs I have used are from Smith & ARROW via their internet store or Ebay listings.  Excellent service and a long lasting quality product.

Suitable grind stones can be purchased from abrasive supply companies listed in the yellow pages.  Small diameter stones are also sometimes available from general hardware stores.

With any of these stones, just make sure you don't exceed the safe rotational speed.

As forces are very low there is no need to overtighten the stones and risk damaging them when mounting on the grinder shaft.

The finish you get will directly depend upon the grit number of the stone.  Finer is obviously better.

TPGs are a not a magic panacea for a better finish unless you go down to a level of stone that is essentially polishing rather than grinding.  A shear tool will give a better finish than a medium grind stone on low/medium carbon steel.

However, the harder the steel, the better the finish for a given grind stone grit.

Grind in both directions

To get a  symetrical finish with fine cross hatching be sure to grind across the job in both directions, and also reverse the rotational direction periodically.

If you only grind in from one end of the job you risk grinding a fine taper due to stone wear, so always adjust and grind in from each end.

The actual grinding pressure is extremely light.  You are not taking off anywhere close to a regular tool cut, only skimming the surface.

So go slow, light, reverse feed and rotation occasionally, and the job should work out well.

Lathe spindle speed

Given that the TPG is spinning at approximately 7k RPM the direction and speed of lathe spindle rotation is pretty unimportant.  However, a slower lathe spindle speed is best to maximise stone coverage.  So slower is actually better.

Grit and abrasive residue

Some hobbyists have a fear of tool post grinders, and comments of "it will destroy your lathe, it's a death sentence" etc  can only leave you wondering if they have any idea of what goes on in a machine shop.

If precautions are taken, grit residue will not be a problem and the lathe will continue to carry out it's intended function for many years.

Using a damp rag to cover surfaces is one way - see below.



If I'm doing a lot of grinding I also use a small flat piece of steel to deflect the sparks and grit away from the lathe - and avoid setting the rag on fire.

In the photo above I would generally place it just where the sparks hit the rag.

The leadscrew is totally shielded, so no problem there.

You can see the amount of residue generated below.



A good vacuum and wipedown will soon clean the unit up again.  Clean the chuck as well.

I use toilet paper to clean the ways and slides.  It's very effective at catching grindings and cuttings and can be disposed of easily.  A re-oil and the lathe's ready to go again.

For older lathes with open gears you may have to put a cover of some sort over them to prevent grit getting into the works.  Modern lathes generally have most moving parts well shielded so this is not an issue.


Summary

Waldown grinders are about as good as you can get, and hold their value extremely well. 


An absolutely top class unit that you will never ever regret buying.





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gloaming_agnet@hotmail.com

South Australia

2014