Trepanning sucks but this tool makes it easy!

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Rich V
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Trepanning sucks but this tool makes it easy!

Post by Rich V »

For me the most onerous machining step in making a can is hollowing out the rear cap where the barrel is attached. It reduces the weight significantly but it is a slow process of either trepanning a circular slot or drilling a bunch of holes.
Traditional trepanning uses a 'single point' tool ground to the specific size and curvature to match the radius of the cut.

Image

Commercial ones, like above, are available but expensive or you can grind a HSS tool yourself. The problem I have had with these is chatter during the cut unless you have a very rigid setup.

Having had my fill of traditional trepanning I tried a different approach - annular cutters

Image

They are available in a great range of sizes and cut with zero chatter.
I recently started with a 1.5 in 17-4 rod and in two steps had trepanned out my slot for an end cap suitable for a 1.4in OD tube threaded to 5/8 24 TPI.
I used these two cutters:
1-1/4", 3/4" Weldon Shank 1" depth of cut.
https://www.amazon.com/Accusize-Tools-A ... g=pda0e-21
1-1/8", 3/4" Weldon Shank 1" depth of cut
https://www.amazon.com/Accusize-Tools-A ... g=pda0e-21

Since these are available in a lot of sizes they can be adapted to almost any size end cap/thread diameter. The only real issue is they come with a rather short 3/4" weldon shank that can be a challenge to hold in the tail stock of a lathe. I used a 3/4" drill chuck to hold mine and it worked without issue.

Give these a try on your next can, makes machining a lot easier.
poikilotrm
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Re: Trepanning sucks but this tool makes it easy!

Post by poikilotrm »

This thread is not what I thought it was about. :lol:
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Historian
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Re: Trepanning sucks but this tool makes it easy!

Post by Historian »

Rich V.,

Thank you for pointing out this novel tool.
It has added to my knowledge base ... and 'tool-junkie-alert' ...
to my tool collection. :)

Many novel uses immediately spring to mind.

Best.


Learned more about annular cutter here:
<< https://www.youtube.com/watch?v=81b41wcGW7k >>
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Sergeant
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Re: Trepanning sucks but this tool makes it easy!

Post by Sergeant »

You've saved me a lot of research.....
This is something I've been looking for but had put on the back burner.
Historian
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Re: Trepanning sucks but this tool makes it easy!

Post by Historian »

Reviewing related YouTube presentations on cutter
a thought came to mind.

Could these be used to facilitate the machining of a mono-core?

Beginning holes initially cut out using a small diameter bit and then
milling out facilitated?
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Re: Trepanning sucks but this tool makes it easy!

Post by Snake-eater 1 »

poikilotrm wrote:This thread is not what I thought it was about. :lol:
Yeah, I was wondering why someone was starting a thread on brain surgery!
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partsguy22
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Re: Trepanning sucks but this tool makes it easy!

Post by partsguy22 »

annular cutters work very well
however split round hss or carbide blanks can be ground in just a few seconds and are many times more versatile (ie more diameters from the same tool )

edit : to grind tool simply grind off half of the split portion so you are left with a 1/4 pie shaped piece (with just a small amount of back? clearance) with the vertical portion to the center (left lower quadrant of a circle looking from the tail stock) it will also cut radially from the inside out so you can widen a groove

the diameter of the groove must be larger than the cutters original diameter , if you start with a 1/2" tool blank the ID(remember id is the larger and od is the smaller dimension when talking about face grooves) of the groove must be larger than 1/2"
Rich V
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Re: Trepanning sucks but this tool makes it easy!

Post by Rich V »

partsguy22 wrote:annular cutters work very well
however split round hss or carbide blanks can be ground in just a few seconds and are many times more versatile (ie more diameters from the same tool )

edit : to grind tool simply grind off half of the split portion so you are left with a 1/4 pie shaped piece (with just a small amount of back? clearance) with the vertical portion to the center (left lower quadrant of a circle looking from the tail stock) it will also cut radially from the inside out so you can widen a groove

the diameter of the groove must be larger than the cutters original diameter , if you start with a 1/2" tool blank the ID(remember id is the larger and od is the smaller dimension when talking about face grooves) of the groove must be larger than 1/2"
Very true but making the tool was never a problem.Getting a cut without a lot of chatter was elusive and that is on a 13x40 lathe weighing 1200 lbs.
Never had a bit of chatter with annular cutters and they cut fast. For us "amateurs" annular cutters are much more likely to give good performance than hand ground tooling.
Rich V
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Re: Trepanning sucks but this tool makes it easy!

Post by Rich V »

Historian wrote:Reviewing related YouTube presentations on cutter
a thought came to mind.

Could these be used to facilitate the machining of a mono-core?

Beginning holes initially cut out using a small diameter bit and then
milling out facilitated?
Yes they are preferred for drilling holes larger than ~1/2 inch. Much less horsepower is needed and cutting is faster compared to drilling.
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fishman
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Re: Trepanning sucks but this tool makes it easy!

Post by fishman »

Rich V wrote:
partsguy22 wrote:annular cutters work very well
however split round hss or carbide blanks can be ground in just a few seconds and are many times more versatile (ie more diameters from the same tool )

edit : to grind tool simply grind off half of the split portion so you are left with a 1/4 pie shaped piece (with just a small amount of back? clearance) with the vertical portion to the center (left lower quadrant of a circle looking from the tail stock) it will also cut radially from the inside out so you can widen a groove

the diameter of the groove must be larger than the cutters original diameter , if you start with a 1/2" tool blank the ID(remember id is the larger and od is the smaller dimension when talking about face grooves) of the groove must be larger than 1/2"
Very true but making the tool was never a problem.Getting a cut without a lot of chatter was elusive and that is on a 13x40 lathe weighing 1200 lbs.
Never had a bit of chatter with annular cutters and they cut fast. For us "amateurs" annular cutters are much more likely to give good performance than hand ground tooling.
Just cut slower and its a non issue
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Rich V
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Re: Trepanning sucks but this tool makes it easy!

Post by Rich V »

I can cut much faster with an annular cutter that any single point trepanning tool.
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fishman
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Re: Trepanning sucks but this tool makes it easy!

Post by fishman »

Rich V wrote:I can cut much faster with an annular cutter that any single point trepanning tool.
Meh, if you're not mass producing, its not worth the extra tooling imo. If I had one lying around out certainly use it instead though
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partsguy22
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Re: Trepanning sucks but this tool makes it easy!

Post by partsguy22 »

What I was getting at , "amateurs" usually arn't conserned with speed as they are cost of tooling
with an annular cutter you get exactly one groove width and profile
a ground tool however much slower it may be is more flexable
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Re: Trepanning sucks but this tool makes it easy!

Post by cdhknives »

I have a lot less chatter when opening up (boring) the groove wider...it is the plunge cuts that chatter most on my light lathe. I might try one of these cutters to start and set the cut depth, then switch to a boring tool to open up the groove. Interesting thoughts...and I think I have one or two in the pile of bits that came with my lathe. I hope it's sharp... :lol:
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