Machining a tool to make a tool...

Thread Starter

Externet

Joined Nov 29, 2005
1,628
Hi.
Trying to have a tool made, went to a decent machinist with decent equipment and he gave up.
What and how would you suggest this can be done ?
Purpose is to make circular grooves 'gland' in bronze to lodge o-rings.

Source 'virgin tool' is a straight 3/4" carbide router bit to modify. Its dimensions are 0.750" o.d. ; 0.362" i.d.
like ----> https://www.harborfreight.com/carbide-tip-straight-router-bit-set-3-pc-68869.html

Tried to do by hand with Dremel what the machinist could not (internal 0.480" diametre on sketch) but unhappy with results from tired vision and shaky hands :(

Tool.JPG
Left = 'virgin' tool ; right = modified to match measurements shown.

Edit: Is there router bits for carving o-ring glands on the market, istead or reinventing the wheel ?
 
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Papabravo

Joined Feb 24, 2006
16,486
There is a problem with your expectations. Tools are made and then hardened. It is difficult if not impossible to machine an existing tool, except with a grinder. You are going about this in the wrong way. You start with something you can machine and then subject it to a hardening process.
 

jpanhalt

Joined Jan 18, 2008
11,088
1) What machine will you be using? Can you use a centering pilot? Without a pilot, you will need a good mill.
2) With a mill, I would consider a single point cutter. Rough cut the groove, then change to a shaped cutter (HSS or even carbon steel will work)
3) I would grind the cutter, rather than try to machine it.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,628
Thanks, fellows.
:oops:Poor terminology, I assumed grinding was a method of machining; should have said grinding instead of milling to bring to dimensions. May implement a pilot. Grinding internally is what the machinist could not do :(

Waiting for response from a manufacturer, seems there is one...
----> https://www.dixon-lesley.com/groove.shtml

With better search terminology, found some promising candidates as "carbide tipped hole cutters" but of course, no internal dimensions listed...
 

jpanhalt

Joined Jan 18, 2008
11,088
Thanks, fellows.
:oops:Poor terminology, I assumed grinding was a method of machining; should have said grinding instead of milling to bring to dimensions. May implement a pilot. Grinding internally is what the machinist could not do :(
That is why I suggested a single point cutter. You could take a lathe cutter and round its tip. Might even be able to buy carbide inserts with the correct radius.

An alternative to a single point cutter would be a rotary table and a ball-end cutter.
 

shortbus

Joined Sep 30, 2009
8,708
As a retired machinist/die maker, you won't get a good enough surface with that router bit. Carbide is ground with diamond tipped tools/wheels, they don't like to be used held by hand. And yes grinding is a machining method.

The tool type you're looking for is called a "trepanning tool", Didn't look but they should be available for O rings. But they need to be used in a lathe or mill to get a good enough surface finish for an O ring. No chatter marks allowed.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,628
Thank you, shortbus.
Proper terminology makes a difference. 'Trepanning tool' opened new doors to my search. :)

The 'by hand' part was related how I attempted to grind the tool with a diamond Dremel bit. To make the cut, tool will be held by a solid mill.

Edited: The link at post #5 notified me they do not produce such any more :( So am back to modify an existing bit.
 
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shortbus

Joined Sep 30, 2009
8,708
There are companies still doing it. How many of the O ring grooves do you need to make? If only a few a high speed steel tool will work for a long time, that is what most milling cutters and lathe tools are made of. Also you will get a better finish with HSS, since it will be sharper that a comparable carbide cutter. (the last statement may open a big can of worms)

Another name for that type tool is "annular cutter".

I know you can Google but here is a Google search for the tools, lots of places making them even a couple of DIY methods. https://www.google.com/search?client=firefox-b-1-d&q=o+ring+trepanning+tool
 

Wolframore

Joined Jan 21, 2019
2,317

shortbus

Joined Sep 30, 2009
8,708
Thanks. About 50.
Found they have other names, as hawg, rotabroach.
Those are brand names. And I would never use one to cut an O ring groove. They are more for cutting a hole, like a hole saw. You need to look at specs for O ring finishes, they need to be pretty smooth, that's why most O ring tools are single tooth cutters.
 

jpanhalt

Joined Jan 18, 2008
11,088
Those are brand names. And I would never use one to cut an O ring groove. They are more for cutting a hole, like a hole saw. You need to look at specs for O ring finishes, they need to be pretty smooth, that's why most O ring tools are single tooth cutters.
Thanks @shortbus. That's what I said a long time ago. As for the term,"trepanning," I recognized that word from another field (https://en.wikipedia.org/wiki/Trepanning). It has been used to describe the ancient practice of making bore holes "to let the evil spirits out" (e.g., prehistoric skulls with evidence of trepanning/holes). Glad I now know another meaning of the term.
 

Wolframore

Joined Jan 21, 2019
2,317
One final thought don’t forget to break their edge and chamfer this. Otherwise it will damage your o rings and perhaps your fingers. Don’t ask how I know.:D
 

shortbus

Joined Sep 30, 2009
8,708
Thanks @shortbus. That's what I said a long time ago. As for the term,"trepanning," I recognized that word from another field (https://en.wikipedia.org/wiki/Trepanning). It has been used to describe the ancient practice of making bore holes "to let the evil spirits out" (e.g., prehistoric skulls with evidence of trepanning/holes). Glad I now know another meaning of the term.
Where I served my apprenticeship was a small 4 man shop, and they to make money on some jobs would trepan stock when it had a big hole in the part, then use the 'slug' to make other smaller parts.
 

shortbus

Joined Sep 30, 2009
8,708

Thread Starter

Externet

Joined Nov 29, 2005
1,628
Thanks again, shortbus.
The only way I could think of was to make the proper contour cutting tool; to produce a CGA850 profile seat. My goal is not to make the grooves but to make the tool to create them when needed. Not a production type of activity.




And right again; the first attempt produced smaller width than desired grooves.
 

Wolframore

Joined Jan 21, 2019
2,317
I would chuck that up on a lathe and be done with it. One profile tool would make it easier so it's all done on one operation... which will help keep everything concentric. Also just use HSS on brass... carbide not needed. That's probably C360 brass... easy peazy.
 

shortbus

Joined Sep 30, 2009
8,708
I would chuck that up on a lathe and be done with it. One profile tool would make it easier so it's all done on one operation... which will help keep everything concentric. Also just use HSS on brass... carbide not needed. That's probably C360 brass... easy peazy.
Me too for one or two parts. A four jaw chuck and your good to go. It amazed me when I went to work at a couple of big places, how many of the workers couldn't figure out a 4 jaw chuck. They would spend hours trying to get a job dialed in.
 

Wolframore

Joined Jan 21, 2019
2,317
Just measure the center, punch then lightly hold in place with a center or even a drill bit. Dial the chuck in and go to town. I’m inspired to fire up my lathe. I have a project that I’ve been thinking about. Want to replace alll the hardware on my rocket launcher stand with stainless and brass. The exhaust corrodes all the iron and galvanized stuff. Looks like bird poop. The blast shield was replaced with stainless a couple years ago. It wipes off and looks brand new but I used steel for the hardware. It looks horrible.
 
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