This is really a follow on from a post a fair time ago about making flywheels from plate material.
I am just at the moment about to start making three finger engines, two of them have recessed flywheels, and sometimes getting this recess can cause a beginner a few problems, I know it used to cause me a lot of heartache.
Now what I am going to be showing here will cause the purists amongst you to jump up and down, but it is my firm belief that there are no hard and fast rules with regards to grinding tooling, other than if it works, it is right, so what is the problem.
Away we go.
I recessed these two flywheels a couple of hours ago, the one on the right is a recycled one from my mine engine, just with a bigger recess put in. The recesses took less than five minutes per side.
This picture shows the tooling in question, which will be explained a little later.
I just can't get good close up shots otherwise I would have shown you the cutter in full profiles.
This next pic shows the tool in action (but you can't see it, but it does show how the flywheel should be mounted). Mine is mounted into soft jaws, but I would expect you to mount yours into your outside jaws that usually come with the chuck. Do not attempt this with the flywheel on a mandrel, it will not be able to withstand the cutting pressures involved.
Now to the profile of the tool I use, and please remember, this is how I do it, someone else might do it in a totally different way, this one works for me.
Using these rough dimensions (not critical) I can recess to about 250 thou deep, but on a 1/2" wide flywheel I will go a max of 200 thou each side.
There is no easy way to describe how to grind a tool so I am not even going to try, other than to say, keep the tool cool while grinding, grind a bit, quench, if it changes colour dramatically you have already softened the tool, and you will have trouble cutting harder materials.
This tool is designed just like a boring bar with a cutting edge on the right hand side as well, but stuck onto the end of a nice rigid bit of stock rather than on the end of a flimsy thin bar.
The angles shown on the sketch are slightly exaggerated to show where the angles should be to give you cutting clearances, somewhere around 5deg. for each one should be ok. The top face of the cutter should be totally level.
The way to use the tool is mount it very close into your holder, this will keep vibration to a minimum. At the same time square the face of the tool to the job, and get it bob on centre height or if you can't, just slightly below, on no account go higher.
I use a saddle stop for my in cutting, but you might have to lock your saddle and put the infeed in using your compound slide.
So, starting at the outside edge of your recess, minus about 10 thou, plunge straight in to your chosen depth minus about 5 thou, retract, move across just less than the width of the cutter and plunge in again. Keep doing this until you are about 10 thou from the size of your centre boss and retract.
Now you are going to do the finishing cut.
Saddle still locked, bring the tool out to your outside edge of the recess, then wind in using the compound to your final depth, then wind across with your crosslide and carry on until you hit your size for the boss, then retract, bringing the boss to correct size.
If you have any slight chatter marks, these can easily be cleaned up with a bit of emery or wire wool.
My tool has made dozens of recesses in all sorts of materials, mainly non ferrous, but has done mild steel on occasions, and stainless just the once (which I don't want to repeat) and the tooling is still like new, just a slight stone up with an Arkansas stone before use keeps it razor sharp.
Keep the chips flying
John
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