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Treppaning Insert Tool

Kevin T

Stainless
Joined
Jan 26, 2019
I am looking at a bunch of different ways to trepan a cast iron chuck back. Its going to be about 5 1/2" finished diameter and its aout 1 inch thick. I tried a couple of home made HSS cutters but none seem up to the task. I am going to purchase a holder and some inserts to get it done. Have any of you guys used these and can offer some words of wisdom so I make the right purchase the first time?
 
you might get more traffic in the General forum, I've read several posts over there about insert trepanning tools.

What didn't work with your HSS tools? Trepanning tools are relatively straightforward to grind but there are a few things that can trip you up. Last time I did some trepanning it took me a couple of goes (and broken tools) before I found the right combination of angles. 1" isn't too bad at all, especially if you're starting with a 1/2" blank. Worst case scenario you can grind a shorter stouter tool and do it from both sides if you can hold the work that way.
 
you might get more traffic in the General forum, I've read several posts over there about insert trepanning tools.

What didn't work with your HSS tools? Trepanning tools are relatively straightforward to grind but there are a few things that can trip you up. Last time I did some trepanning it took me a couple of goes (and broken tools) before I found the right combination of angles. 1" isn't too bad at all, especially if you're starting with a 1/2" blank. Worst case scenario you can grind a shorter stouter tool and do it from both sides if you can hold the work that way.

Thanks I'll poke around in there. I was trying to use a 1/4 HSS blank bit that I relieved but the material was just too skinny to make the cut. Lots of chatter and generally not good. I don't have the luxury of being able to grind a bunch of test tool shapes especially relieving a lot of material since I store my precious motorcycles and car, etc in my shop/garage.
 
1/4" blank is too small, you need a 3/8" tall blank at minimum and ideally 1/2". Mine is ground from a 1/4x3/8" blank - I use a dremel cut off wheel to get rid of the bulk of the material, then a bench grinder to shape. Tool needs a slight taper on both sides going from tip to tool post (looking down), the outside side needs to ground in a curve that's slightly curvier (?!) than the diameter it's going to be cutting at and you need ~5deg front relief under the tip of the tool. I ground the front of mine at a slight angle so the outside corner of the cutting edge is a wee bit in front of the inside corner. Quick zip with the dremel to give a bit of back rake/ chip breaker to the cutting edge and you're done.

For an inch deep I'd start with a 1/8" wide cutting edge to start with so that it doesn't get too thin at the back (with the slight taper for clearance) that it chatters and snaps. Run REALLY slow (50rpm at the diameter would be nice) with a fairly heavy feed and it should produce a nice curl out of the cut in steel.
 
1/4" blank is too small, you need a 3/8" tall blank at minimum and ideally 1/2". Mine is ground from a 1/4x3/8" blank - I use a dremel cut off wheel to get rid of the bulk of the material, then a bench grinder to shape. Tool needs a slight taper on both sides going from tip to tool post (looking down), the outside side needs to ground in a curve that's slightly curvier (?!) than the diameter it's going to be cutting at and you need ~5deg front relief under the tip of the tool. I ground the front of mine at a slight angle so the outside corner of the cutting edge is a wee bit in front of the inside corner. Quick zip with the dremel to give a bit of back rake/ chip breaker to the cutting edge and you're done.

For an inch deep I'd start with a 1/8" wide cutting edge to start with so that it doesn't get too thin at the back (with the slight taper for clearance) that it chatters and snaps. Run REALLY slow (50rpm at the diameter would be nice) with a fairly heavy feed and it should produce a nice curl out of the cut in steel.

Thanks I may try this. I have one 3/8" cutter that is shapped correctly but not relieved enough to make the whole cut so I haven't tried it.
 
I'm cutting, or attempting to cut, a thru groove to bring a 8" diameter chuck back down to 5 1/2" diameter.
I'm missing something. . :dunce: (<--- that's me)
Why not just turn the OD rather than messing around with this?
Trepan tools can take lot of time to get right and are not very fast cutting.
Generally they are avoided if possible. Not to say I dislike them as I make many thousands a year for various uses.
The outside does not need to be radius, a primary and secondary flat works just fine. One just has the clear the heel at the bottom of the tool in the cut radius. A quick sketch in CAD or even MS paint shows where and angle.

Do you have a standard carbide insert holder for OD work?
I know cutting less material is less total "work/HP/metalcutting" done but sometimes making a special tool is more time spent than a brute force attack of turning all into chips.
8 to 5.5 is a inch an a quarter per side at only one inch thick.
KISS.
Bob
 
Matt,
Put 4 to 5 degrees on the inside. It may work better. The used tool is talking to you in pic 2.
That is what I love about used tooling and in so many cases I ask for used but not broken. They tell a story about why did I die.
Bob
 
I'm missing something. . :dunce: (<--- that's me)
Why not just turn the OD rather than messing around with this?
Trepan tools can take lot of time to get right and are not very fast cutting.
Generally they are avoided if possible. Not to say I dislike them as I make many thousands a year for various uses.
The outside does not need to be radius, a primary and secondary flat works just fine. One just has the clear the heel at the bottom of the tool in the cut radius. A quick sketch in CAD or even MS paint shows where and angle.

Do you have a standard carbide insert holder for OD work?
I know cutting less material is less total "work/HP/metalcutting" done but sometimes making a special tool is more time spent than a brute force attack of turning all into chips.
8 to 5.5 is a inch an a quarter per side at only one inch thick.
KISS.
Bob

Your science sounds tight, but....in my previous cutting of cast iron chuck backs I was making magnetic dust not chips! I was making it by the truckload and I want to limit how much of this stuff I have to deal with. It sounds like you are suggesting a much heavier cut that I have not tried with this material, and if I read correctly I can expect actual chips! Sounds like you are a fan of carbide for this task to mow down the outer diameter. I am tooled up for this. I'll need to do some searching. in the meantime if anyone has links that can get me up to speed more quickly I would appreciate it.
 
Matt,
Put 4 to 5 degrees on the inside. It may work better. The used tool is talking to you in pic 2.
That is what I love about used tooling and in so many cases I ask for used but not broken. They tell a story about why did I die.
Bob

the other end tells the story of the grind that didn't work :) This one works pretty nicely to be honest, though it is fairly short. The difficulty I had was that to get a longer reach and maintain side clearance on both sides (probably only a couple of degrees here tbh) the tip had to be wider and the wider the tip the more problems I had with chatter on my small'n'light lathe. Bloody trigonometry. Also depends on the radius being cut too - the larger the radius the less the side (heel?) clearance needs to be = taller stiffer tool. It's a fun grind to think about, lots going on.

Also, another benefit for home hobby types is that you end up with material that can be used for something else - in Kevin's case a 1" thick 8" diameter cast iron ring. That'd make a great flywheel rim for a model engine builder :)
 
..."Also, another benefit for home hobby types is that you end up with material that can be used for something else - in Kevin's case a 1" thick 8" diameter cast iron ring. "... :)

HA! you guys are great. I was getting ready to just mow that OD down and forget about the trepan but then the allure of having a cast iron ring to play with surfaced. Now I am in a holding pattern again. Anyone want to buy a cast iron ring? LOL Wait NFW...I couldn't let it go. I might want to make a big boy cross feed turning wheel of some sort!:D
 
Well I punted and mowed down the OD. i hadn't used the lathe for a few weeks so I guess making chips won! I decided to take some time to really see what I could get away with on material removal. I remembered that the last time I turned a chuck back I made a lot of dust so I rigged up some protection for my lathe in the form of a box. It worked pretty good with a vacuum nozzle attached to the compound.

image018.jpg

I have a negative rake carbide tool holder that I don't have much use for but I found that if I put in a positive rake carbide insert I can get good results in my old SB.

image004.jpg

I took a bunch of passes to figure out the best plan of attack. It turned out that a .075 cut on backgear position 1 was perfect! This is a 125 spindle speed.
I had pushed it up to about .085 but it was getting noisy so I backed it down to .075.

image013.jpg

Got some big rings on the cut as I passed though the material.

image020.jpg

image021.jpg
 
I found this thread interesting as I was finding myself in need of a tool to do some trepanning which I hadn’t done before. Good information, thanks! But the person who makes thousands of tools every year... let’s see, seven days a week, hmmmmmm, six tools per day to make a few thousand in a year. Must Really be good at it. (Sorry)
 
I used a 4” hole saw to cut through an old back plate. I made a spindle thread protector out of the center Slowest backgear and 30hz on the VFD. Worked surprisingly well. Make sure to back up the tailstock chuck to keep it from spinning. Also make sure one of the holes in the side of the hole saw is down so the cast iron dust falls out.

Ended up with a 1” wide cast iron ring that I mounted the MLA faceplate rough casting to so I can hold it with my four jaw chuck. I haven’t started machining the casting yet but it should work good.

Hope this helps.

Ben
 








 
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