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Member postings for Michael Cox 1

Here is a list of all the postings Michael Cox 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Rear mounting parting-off tools
13/10/2009 13:13:32
Interesting comment David and I have seen the same mentioned before. However, I cannot see that the fact that the cross slide lifts up into the dovetail is any more rigid than when the cross slide is pushed down onto the solid surface under the cross-slide.
The main reason why a rear toolpost is more effective is, in my opinion, that it is less rigid and in the event of a "dig in" the toolpost can deflect upwards and backwards to release the dig in.
With  a front mounted toolpost, in the event of a dig in, the tool is dragged round under the workpiece and it is jambed between the the workpice and the cross-slide causing it to dig in further.
Thread: Case Hardening
09/10/2009 16:27:59
Hi Peter,
The use of coaldust is not recommended. It has a high sulphur content that will adversely affect the case hardening. Fine powdered charcoal will work ok especially if mixed with sodium bicarbonate (baking soda). A 90% charcoal dust with 10 % sodium bicarbonate works well for pack carbonising.
Thread: Rear mounting parting-off tools
09/10/2009 16:22:32
Hi Tony,
There are two main advantages to a rear mounted parting off tool. Firstly, with a conventional front mounted tool, if it digs in the tool tends to go under the work piece and is wedged between the workpiece and the topslide because the lathe is very rigid and this tends to make it dig in deeper. If the same happens on a tool mounted in a rear toolpost then the tool tends to ride up on top of the toolpost and the toolpost is deflected away and hence the tool tends to "undig" itself.
The second advantage of the rear mounted toolpost is that the chips tend to fall away rather than collect in the parting groove so there is much less likelihood of the tool jamming in the slot due to chips wedging between the tool  and the groove.
If you have a flange mounted chuck and can reverse the drive then the same result can be had by mounting a parting tool upside down on the front side of the lathe. If the chuck is mounted on a screwed mandril nose piece this cannot be done because the chuck will tend to unscrew.
I have fitted a rear toolpost to my Asian minilathe and the difference in parting performance is amazing.
Thread: Diamomd tool holder
05/10/2009 15:11:50
In view of current interest in this subject and also the article in issue 156 MEW I thought others might be interested in yet another design of tangential toolholder.
This photo shows the completed toolholder mounted in the lathe:

It is easy to see the 12 degree inclination of the tool in the forward direction in this photo.
The next photo shows the end of the toolholder shank:

This shows that the shank is trapezoidal and this inclines the tool 12 degrees from the vertical towards the head stock. The next photo also illustrates this point somewhat more clearly:

The advantage of this mode of construction is that the whole tool is made from a piece of 1/4" plate. It is only necessary to mill the slot for the tool at 12 degrees and then file or mill the shank to have the 12 degree trapezium angle. These are very straightforward operations and the whole tool can be made in 3 hours.
I hope this is of interest.
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