Trepanning

[trg-s338]

Folks,

Can I please get some information on trepanning? I'm not sure if I'm using the right terminology but from my readings on the net, this process involves feeding a specialized tool (groover?) on the face of the work and actually cutting out the "core", for lack of a better term. Is this correct? Is it difficult to do with its own set of considerations such as with cut-off tooling? Why is it done? To achieve the bore and save the outer or center material for other use instead of turning said material into chips? Maybe I'm not getting it, is it only for grooving the face of the work and not really for "coreing"? I've never done it but it would seem to me that trepanning, if my understanding is correct, would be most useful in the home shop. I've occasionally had to use available stock laying around in my garage that is larger than what I need and had to turn material down to size and waste a lot of solid to chips when that could be used on other projects in the future. As a newbie, I'm probably lost and don't know what I'm babbling about so please excuse me. I'm not sure if my question is clear either. Thanks for your time.

 

[Goldstar31]

Trepanning is merely cutting into a bit of metal- or a skull if you are an Ancient Egyptian with a tool that removes a relatively small track of metal.
There has been a lot of prattle about parting off and really a trepanning tool is nothing much different. Clearly, there is a need like in boring and turning to avoid scuffing or rubbing the flanks of the tool against the metal which you want to leave.

It is best thought out on paper at the same size as the job to trepan. You draw a circle at the diameter wanted and then you draw in your tool blank at centre height. You will quickly see that the flanks of the tool have to be ground to follow the circumference drawn. A lot of workers will put curved sides on the tool but if you haven't any fancy grinding skills you can cheat by having straight tapered sides.

All that you have to remember is that a new tool has be ground up or the old tool altered to suit a new diameter.

It sounds a lot of new learning but really all that you have to remember is mentally shaping your tool to avoid catching the metal that you want to keep.

Cheers

Norman

 

[Tony Wells]

So far, shallow trepanning has been described accurately. It can be done on a mill to cut our discs, or to create relatively large holes in thin sheet or plate. Either way, material can be conserved by using this method. Realistically, 1.000" would likely be a practical limit due the the rigidity required. Rigid tools would normally be thick(wide), and require horsepower and a stout machine. Depending on just what machine you have, the limits could change. On the other hand, small, bench machines might not be suitable at all for much trepanning.

Industrial trepanning is commonly used on workpieces on the order of 30-40 feet long (or more) and anywhere from 6" diameter up. Yes, the core material can be saved and is sometimes sold back to the supplier if this is being contracted out to a deep hole shop. Inside trepanning leaves the core material for going back into stock. It is a known chemistry, but usually the heat treat is done again, or perhaps for the first time if the material is trepanned in annealed condition. In the oilfield, literally hundreds of miles of trepanned material is used in drill collars, adapter subs, and other drill string components.

Mumbles reference to a face grooving tool made by Iscar works well for shallow trepanning. I have one, and have used it for cutting discs of 3/8" thick material.

 

[trg-s338]

Thank you all for the schooling on trepanning. It will still be useful to me up to 1" with the right tool, power and rigidity if I hear correctly. Thank you for the referenced tool also, I'll have to get that on the next budget.