Altering a tool shape

[spike7638]

I'd like to take a plug-cutter (a tool for making wooden plugs that then are inserted into holes to cover up fasteners) and slightly alter it. Here's a picture of a plug-cutter set, so that you get the idea:


The resulting plugs --- created by plunging the cutter into the face of a board, and then bandsawing the board to make the plugs call out --- are more or less cylindrical. The fancier plug-cutters actually make plugs that are slightly chamfered on the very top (if you plunge deep enough).

I need some plugs that are "half-inch oversized", i.e., the plug has a diameter of about 0.53 inches. In fact, I'd really like to make a plug that tapers from 0.55 down to about 0.51. (Some plug cutters already have taper, but none are quite this size, alas).

I thought that perhaps I could start with a plug-cutter like the one above, and on a lathe, remove some of the material inside using the compound -- is that the right term? --- to produce the taper, and something like a boring bar to hold a bit that'd do the cutting.

But I expect that the cutter is made of tool steel and very hard, so maybe this idea is just stupid. Or maybe it needs to be ground (which is probably beyond my skills). Or maybe I should start from scratch and make something that does the job well enough to produce 8 or 10 plugs, which is all I need.

Can anyone give me advice on the feasibility of the "modify an existing cutter" approach, and how I could go about it?

 

[francist]

The plug cutters that I have like that are very hard -- too hard to modify on the lathe as is I think. However, they are not High Speed Steel which suggests that they could be softened enough to to be cut with your boring bar. If you don't need many you may get away with not even having to harden the cutter again after you've modified it.

Grinding is the other option that comes to my mind, but finding the appropriate sized and shaped point could be a pain. On the other hand, might be less effort in the long run than going the heat treatment route. An inexpensive grinding point could be dressed into a slight taper easily enough.

-frank

 

[JimDawson]

Depending on what equipment you have, making a tool post grinder would be my first choice.

Here is how I did mine. Air die grinder from Harbor Freight.

 

[Groundhog]

How about cutting the profile of your plug from a larger diameter dowel (5/8) on a lathe? Eliminate the plug cutter.

 

[JimDawson]

How about cutting the profile of your plug from a larger diameter dowel (5/8) on a lathe? Eliminate the plug cutter.

That is way too simple

 

[francist]

Plug cutters cut cross-grain.

-frank

 

[RJSakowski]

Turning or grinding an interrupted cut can cause a rounding over of the cutting edge. This will prevent the plug cutter from cutting properly. Whenever I have tried a modification like this, I take a light cut and have the cutting edge be the trailing rather than leading edge. Grinding would be preferable to turning or boring.

 

[spike7638]

Thanks, everyone, for the ideas. I'm now wondering whether a die-grinder might do the job, with the original cutter chucked in my drill-press (which I can do at home, rather than setting up something messy like this in the shop at work). I'll have to experiment.

The "use the lathe to reduce a larger plug" idea is a nice one, and I could cut some 5/8 plugs and try this...but as Frank points out, the grain runs perpendicular to the lathe axis, and this leads to three problems: (1) irregular cuts producing elliptical cross-sections, (2) a tendency to "grab" at two points in the cycle, and (3) a tendency to split along the grain. (Indeed, in teak, which is the wood I'm using, this along-the-grain splitting even happens sometimes with a top-notch plug-cutter.

Then again, starting from a 5/8 plug and doing something like sanding ... perhaps a dremel hooked up to counter-rotate and sand as the drill press is turning the plug .... could conceivably work. I guess it's time to go back and noodle a bit more.

 

[RJSakowski]

I had to turn some mushroom shaped plugs a couple of years ago. The grain would chip out or if I tried to remove the plug (they were meant to be removable), the lip would break off. I saturated the blanks with super glue and let them cure overnight. This gave me a much stronger plug. They were roughed out on the lathe and the cap machined using the CNC mill with a ball end mill, followed by sanding in the lathe.

 

[brino]

My first choice would be what @Groundhog suggests and simply turn the part you need rather than a custom cutter to make a part.

My second choice would be to forget trying to modify a hardened, commercial plug cutter and make your own.
Since you need less than a dozen, even unhardened steel should work.
Maybe start with a piece of pipe with an ID that meets the minimum diameter, and cut/grind the taper to suit.
Then using a grinder/dremel cut the gaps for the cutter teeth.

Good Luck and be safe!
Please let us know how you make out.

-brino