# Lathe - Internal threading tool DIY or purchased?



## PurpLev

I made an external threading tool by grinding an HSS blank to a 60 degree point and now am at a point I would like to have an internal threading tool as well. I have O-1 tool steel I can use for the shaft and have seen some posts by people making their own internal thread tools using drill bits as the cutting edge. looking online at alternatives for purchased internal threading bars is a bit daunting as they use different inserts which I am not sure what the differences between them are which is another reason I'm driven to make my own ($$$ being the other reason since I already have the material at hand).

what is your take on internal threading? DIY? purchase? 


if DIY - how did you make it - got any pictures to show for it? any tips or things you'd do differently?
if purchases - which one are you using ? what is it's benefits (insert type and whatnot)?

:thinking:

Thanks in Advance,
Sharon


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## Tom Griffin

Just get yourself an assortment of nice rigid boring bars and grind your own HSS threading bits. Making boring bars yourself is a pain because of the square hole for the bit and the fact that they need to be hardened and tempered. I like the style shown below, they are cheap, readily available, and versatile since you are grinding your own bits.

Tom


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## PurpLev

TLGriff said:


> I like the style shown below, they are cheap, readily available, and versatile since you are grinding your own bits.



Where did you get those from? and what bits are you using in them? 1/4"x1/4" HSS?


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## Tom Griffin

PurpLev said:


> Where did you get those from? and what bits are you using in them? 1/4"x1/4" HSS?



I have several like the ones shown in the pic. The smaller one takes a 1/4" bit and the larger one a 5/16'. *McMaster Carr* carries them and the bits. Enco probably has them but I can never seem to find my way around their crummy web site. MSC also has them but they looked to be more expensive than MC.

Tom


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## Tom Griffin

etard said:


> For cutting internal threads on a small lathe, is HSS preferred over Carbide?



High speed steel should _always_ be the first choice for the home machinist. It is cheaper, easier to work with, provides a better surface finish and is much more versatile than carbide tooling.

Carbide would be appropriate for production or machining hard or difficult to machine materials on rigid machinery.

Tom


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## jocat54

I have made a couple following the advise on this site and they work really well. You can make them whatever size you want and it doesn't take long to make them

http://madmodder.net/index.php?topic=3523.0


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## PurpLev

etard said:


> Now there's a good idea Blue, seems like somebody would already make those using carbide tipped.
> 
> For cutting internal threads on a small lathe, is HSS preferred over Carbide?
> 
> By the way, I just won a few of those on ebay, If you like I can send you one, and if you don't like it, just send it back.
> 
> http://www.ebay.com/itm/14076517798...X:IT&_trksid=p3984.m1439.l2649#ht_1942wt_1185
> 
> 5 for $25, not bad huh?
> 
> View attachment 37311



yeah, not too shabby - nice. what cutters are those meant to be used with? 

I'm using HSS only (when I got my first lathe it came with a set of brazed carbide cutters that kept on chipping... hated that), I learned how to sharpen them - it's not that difficult, and the cut quality is superb, plus I can always resharpen them, as well as custom shape them if need be. here is a recent sharpened cutter cut finish on CRS (turn+face without locking carriage):


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## PurpLev

jocat54 said:


> I have made a couple following the advise on this site and they work really well. You can make them whatever size you want and it doesn't take long to make them
> 
> http://madmodder.net/index.php?topic=3523.0



Thanks for the link. I've seen this while researching for an alternatives, but to me this one seems limited in it's reach (will bump against the shoulder of the tool for longer threading jobs. is that not so?


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## Tony Wells

What you say is true. It's a matter of trading rigidity for reach, as with all internal tooling. Just try to leave the undercut section as large as practical for the thread you intend to cut. 

That is an old idea, but it does work. Normally, threads do not have a perfectly sharp root, as was pointed out in that thread, and it can be cause for stress cracking in some materials. Not usually a big deal, but worthy of mention.

If you wanted to fancy it up a little, use a 4 jaw and make the cutting disc off-center and you can leave the undercut a bit larger. That precludes using the tool for OD and ID work both. And also what was said about clearance angles is also correct, but for finer pitches, it may present no problem either. Properly done, the 60° angle should be a constant, but the flanks are relieved to allow for the helix angle of whatever thread you are cutting. A little imagination is required to cut this, but it can be done.


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## epanzella

I make my internal threading tools by turning square 01 tool steel round, and then use a 60 degree cutter to make the profile for threading. Next mill it to half diameter. This will give you a cutter with 2 edges but I grind off the back one so it'll go into a smaller bore. Last is heat treating. You can use round stock as well but the square profile gives me consistent rake angle on the tool.






	

		
			
		

		
	
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## bill70j

PurpLev said:


> what is your take on internal threading? DIY? purchase?
> 
> if DIY - how did you make it - got any pictures to show for it? any tips or things you'd do differently?
> if purchases - which one are you using ? what is it's benefits (insert type and whatnot)?



I use bars that accept HSS ground bits, like Tom shows, as well as tool holders for threading inserts.

For small diameter bores, I have a 1/4" bar and a 5/16" bar.  I grind the bits from either round or square HSS blanks.
For larger diameter bores, I have 8, 10, and 12mm bars that take an 11mm IC insert, an a 16mm and 5/8" bar that take a 16mm IC insert.

I prefer the inserts simply because they are easier to use and seem to stay sharp forever.  I use the HSS bits for smaller diameter bores.

Here is a pic that shows the 8mm bar with the 11IC insert and the 5/8" bar with the 16IC insert.  It also shows the 1/4" bar with a bit ground for ACME threads and the 5/16" bar with a bit ground for 60 deg threads.


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## magicniner

These days I use Iscar MGCH 06 and MGCH 08 bars with LH threading inserts and thread from the bottom of the hole outwards on most jobs.


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