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The task of parting off is always one that stretches your lathe to the full.
If the tool is situated in the normal (front) toolholder and the tool digs in, then the tool dips, and in doing so moves forward, digs in harder and either the lathe has to stop or something has to break. Parting off from the rear however means that if the tool starts to grab, the rotation of the work tends to lift the tool and move it away, thus automatically relieving the tendency process of "digging in".
The toolpost shown here is based upon a design by George Thomas as published in his book "The model Engineers Workshop Manual". The design holds two parting blades of 3/32" and 1/16" although it can be made to hold a parting blade on one side and a chamfer tool on the other side. I made mine from a kit obtained from Hemingway Kits and it works a treat. (www.Hemingwaykits.com). The top part is indexed on the base and can be quickly turned round to present the alternative tool to the work. When not in use I turn the head through 90 deg. to move the "sharp bits" away from the working area. I leave the unit permanently in place on the back of my (long) cross slide so it is always ready for use. It only gets removed when using the taper turning attachment.
Let me first say that the attachment is superb. However if you are using a Myford Collet system, be aware that the lathe saddle will not move sufficiently left to allow this device to part off right up to the mandrel nose. The second limitation - if you can call it that, is that the parting diameter is limited to a maximum of about 2". This is limited by the reach of the tool when set to centre height. Also the fixing bolts start to get in the way at above this diameter.
REAR TOOL POST
For Myford Lathe
|Origins of the Name|
|James Haythornthwaite 1810|
|Rotary Table Adapter|
|Rear Tool Post|
|Weaving the Cloth|
|Grenfell at Speed|
|Grenfell High Places|