# Trepanning



## Magnum (Sep 4, 2011)

Looking around for what the proper lathe tool I need for trepanning a part on my lathe. The part is 2 IN OD with about a .5 IN OD boss in the middle. I need to remove the material and leave the boss and about .25 IN thickness wall at least .75 IN deep.

Material is 7075 AL.

Can this be done with the same tool used for grooving? Just a larger cut width?


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## Tony Wells (Sep 4, 2011)

You could do it with face grooving tool. You don't need to cut the full width all at once. Make sure you have clearance on both sides of the tool, most notably the outside. The tool should be widest at the end, obviously, so it doesn't drag as you plunge. Take several plunge cuts, then traverse across the bottom of the grove, leaving a smooth face. It will work out easily in aluminum.


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## Magnum (Sep 4, 2011)

Thanks, that is what I was thinking. One thing I did forget to mention was I will need a small radius at the bottom instead of a sharp edge. So I need to look for a grooving tool with radius-ed edges or bite the bullet and by a grinder and try and make one.... Any excuse to buy a new machine 

I could make the part on the CNC, but its a lot easier/quicker to set the pieces up on the lathe.


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## Tony Wells (Sep 5, 2011)

Depending on what it has to look like, you also could consider doing it on the mill with a rotary table. An end mill with radiused corners would give you what you describe. Or, depending on what radius you want, perhaps a ball nose end mill for the inside and outside cuts, and a plain end mill down the middle.


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## Magnum (Sep 5, 2011)

Surfaces need to be smoothed as they will end up being a mating surface for a part that will slide up and down the surface. I will probably order a grooving tool later tonight and try next week. I have parting tools but they are angled for parting, should probably use one with a full with cut.

The ISCARS look nice, but dang are they expensive!


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## Blogwitch (Sep 5, 2011)

For trepanning as you require, you will need to grind up your own tool.

It is very similar to a boring tool, but has another cutting edge on the other face.

That allows you to plunge cut the first side (outer edge), then another plunge cut (for the inner boss) then just do more plunge cuts to remove the bit in between. Then one final facing cut by plunging in at the outer face, clean up the bottom and when retracting at the boss it cleans that up as well. I use this method all the time when making flywheels for models.

See picture for grinding info

John


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## Tony Wells (Sep 5, 2011)

If you'd rather buy that make, I recommend Iscar. I use one of theirs.

http://www.iscar.com/Ecat/familyHDR.asp/fnum/169/app/54/mapp/TG/GFSTYP/M/type/1/lang/EN

You pick the radius range for your part. It uses common cut-grip inserts.

There is another way to make one if you have deeper needs. It requires a round bit of tool steel. I have one here somewhere I made years ago out of CPM-10V. Essentially, it is turned round, slightly smaller than your major diameter, and bored eccentric slightly larger than your minor diameter, and deeper than your proposed face groove. Mill a slot on center all the way to the front end with the edge at the thickest part of the eccentric. Mill away about 75% of the tube you've made, leaving plenty of support under the cutting edge you milled. Heat treat. Grind the cutting edge and you will have what is similar to a single tooth hole saw. It is very rigid and will cut a substantial depth with little deflection. 

As a QDM, I have taken an end mill shank and simply ground it to the half way point on it's diameter. It then automatically has clearance on both inside and oustide. A little front rake and relief, and presto, a trepan bit.


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## Magnum (Sep 5, 2011)

Thanks, I am still debating on going ahead and machining this part. It's still being designed but it looks like I need flat edges on the left side, so I could only trepan out so far then put on the CNC to create the cross cuts.

A picture is worth a lot so here is a picture and it is in no way complete in detail. Still a lot more to go on this one.






			
				Blogwitch link=topic=3394.msg24472#msg24472 date=1315236016 said:
			
		

> For trepanning as you require, you will need to grind up your own tool.
> 
> It is very similar to a boring tool, but has another cutting edge on the other face.
> 
> ...


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## Magnum (Sep 5, 2011)

Thanks for the link, I do not own any ICARS but do like what I have heard about them. I may go ahead and order one just to have around. Is there a good source for those? I can;t find those numbers on enco or mscdirect.... 

I haven't had much luck using end mills on the lathe yet. When it comes to the lathe I am very much a newbie! So much I do not even have a grinder yet or many tools for it. So far I have only used it to make spacers 







			
				Tony Wells link=topic=3394.msg24476#msg24476 date=1315238818 said:
			
		

> If you'd rather buy that make, I recommend Iscar. I use one of theirs.
> 
> http://www.iscar.com/Ecat/familyHDR.asp/fnum/169/app/54/mapp/TG/GFSTYP/M/type/1/lang/EN
> 
> ...


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