Shaping 60 Degree thread cutter

[Bentwood]

On Center

I have worked for a large aircraft company and worked for an engineering group and did machining for them about 45 % of the work involved threading almost every type of material you can think of most of it was single point threading with HSS or carbide inserts or braised carbide We set every tool on center and never had any problems on every size lathe from 9" swing to 16" swing.Slow feed rates for HHS. and higher speeds and feeds for carbide.95% had Positive Back rakes and Positive Side clerance.

 

[alinwa]

This is a good thread.



al

 

[Bnhpr]

Thanks to all for the input, much appreciated.

I was interested reading of having the tool above centre, I have been threading on centre, to be honest I would be too embarrassed to post a picture of my end result, that was with an insert, I was threading a 1/2" UNF, just for the practice, seems to have a look of galling.

My Harrison M300 is a Metric machine, so I have to keep the lead screw engaged throughout the threading process to thread imperial.

I will attempt to thread with the insert slightly above the work piece, I was threading at a speed of 50 something rpm, is this too fast.

Many thanks Ian

Not too fast at all....

You should see a CNC lathe thread!!

Is your compund rest over at 30 deg?

Do you have some positive rake in your tool?

Negative rake in a threading tool leaves a shtty finish on anything except brass IME. A lot of machine tool manuals call for negative rake...

Threading should be smooth, quiet, and leave a clean chip, the tool should not growl at you if it is sharpened correctly.

Ben

 

[Reynard]

Not too fast at all....


Is your compund rest over at 30 deg?

Do you have some positive rake in your tool?

Negative rake in a threading tool leaves a shtty finish on anything except brass IME. A lot of machine tool manuals call for negative rake...

Threading should be smooth, quiet, and leave a clean chip, the tool should not growl at you if it is sharpened correctly.

Ben

Hi Ben

The compound rest was set at 29 Deg. I had read on a web site that you should set to 29 rather than 30, there was a reason for it.

The Sandvick threading tool that I am using has an metal shim underneath the threading insert, I am sure this is to set the rake, I can only guess that the rake insert is negative, as the threading insert points down at the tip. I will go now and take a pic of the threading tool, to show rather than try explain.

Ian

 

[Reynard]

http://benchrest.com/forums/attachment.php?attachmentid=7429&stc=1&d=1237099738

Hope this pictures shows better than I can explain.

I am looking at a Multifix tool post on ebay to replace the basic tool holder that came with the lathe.

I have just did a google search for tool rake and read a very good easy to understand article by J. W. (Dub) Thornton at
http://groups.yahoo.com/group/7x10minilathe/message/67226

I know now that I have negative rake on my tool holder, I take it I will have to get the positive rake shim for the tool holder in order for the threads to be cut cleaner. It is staring to fall into place.

Ian

 

[Bnhpr]

http://benchrest.com/forums/attachment.php?attachmentid=7429&stc=1&d=1237099738

Hope this pictures shows better than I can explain.

I am looking at a Multifix tool post on ebay to replace the basic tool holder that came with the lathe.

I have just did a google search for tool rake and read a very good easy to understand article by J. W. (Dub) Thornton at
http://groups.yahoo.com/group/7x10minilathe/message/67226

I know now that I have negative rake on my tool holder, I take it I will have to get the positive rake shim for the tool holder in order for the threads to be cut cleaner. It is staring to fall into place.

Ian

The Sandvik tool system consists of the insert and tool holder. sandvik tech support can probably help you. It gets complicated with feeds, inserts and workpiece material.

I would suggest you contact them. With the p/n's of your insert and holder. They will advise if your setup is correct.

Or, spend 3 quid and buy a 5/16" HSS blank and grind your own like I have in my pic.

Ben

 

[Reynard]

Or, spend 3 quid and buy a 5/16" HSS blank and grind your own like I have in my pic.

Ben

Hi Ben
I have ground 5 HSS blanks to a 60d point, just have to grind the relief and rake onto them, the input from the members and what I have researched via Google has helped me to understand what has to be ground off and more importantly the reason for this.

Thanks for taking the time and patience with a newbie.

My wife's father was a lathe operator since leaving school, he then got promoted to a job within the company where he never touched a lathe, He inspected the work of the other lathe operators and made sure everything went ok.
When I first purchased my lathe , I asked if he could show me how to operate it, when he looked at for the first time, he said he had never worked on a lathe as modern as it, all the lathes he had worked with were over 100y old, I had to end up showing him how it worked (he is 75, so has a good excuse).

Ian

 

[JerrySharrett]

The Sandvick threading tool that I am using has an metal shim underneath the threading insert, I am sure this is to set the rake, I can only guess that the rake insert is negative, as the threading insert points down at the tip. I will go now and take a pic of the threading tool, to show rather than try explain.

Ian

Ian, the metal shim you speak of is called a "shim seat". It is there to protect the tool holder when the cutting insert breaks or you crash it, and it will break and you will crash it!!

. A tool holder like you picture costs about $50-$80 USD. A shim seat would cost about $2-$3 USD.

 

[Bob Kingsbury]

Jerry Sharret

This post, began from a fellow that wanted to know how to grind
H.S.S. tool bits for threading. Technology will take you to many
different set-ups depending on equiptment and material. H.S.S.
differs in many ways from inserts. When I say slightly above center,
that is not .060, but maybe .005 or .010. A tool bit ground precisely
at 60 degrees, no longer cuts a 60 degree thread above or below center.
The change is in minutes, maybe down to seconds, but no longer 60.
Today nearly all production work is done with carbide inserts,or
other similar types of tooling, but that is not common to all gunsmiths.
I don't have room for a turning center at home. There still is a place
for H.S.S and they serve gunsmiths well.

 

[JerrySharrett]

This post, began from a fellow that wanted to know how to grind
H.S.S. tool bits for threading. Technology will take you to many
different set-ups depending on equiptment and material. H.S.S.
differs in many ways from inserts. When I say slightly above center,
that is not .060, but maybe .005 or .010. A tool bit ground precisely
at 60 degrees, no longer cuts a 60 degree thread above or below center.
The change is in minutes, maybe down to seconds, but no longer 60.
Today nearly all production work is done with carbide inserts,or
other similar types of tooling, but that is not common to all gunsmiths.
I don't have room for a turning center at home. There still is a place
for H.S.S and they serve gunsmiths well.

WOW, I didn't know that!!!

 

[Dave Milosevich]

It's the helix angle that needs to be adjusted for...

http://benchrest.com/forums/attachment.php?attachmentid=7429&stc=1&d=1237099738

I know now that I have negative rake on my tool holder, I take it I will have to get the positive rake shim for the tool holder in order for the threads to be cut cleaner. It is staring to fall into place.

Ian

...with "shims" or anvils.

If one is going to use laydown inserts for threading, here are some links to one of the more popular manufacturer's relevant catalog pages. The "shims" or anvils as the manufacturer calls them, are important if the range of threads being cut falls outside the manufacturer's default tool holder pocket angles. If you click on the link labeled "Anvils" at the following post, Threading Inserts ,it is easy to see how the helix angle changes with thread pitch and how it interacts with work diameter. Anvils are supplied to cant the insert to line up with the thread helix. The rake angles are usually features incorporated into the insert itself.

FWIW

 

[WSnyder]

Hi Ben

The compound rest was set at 29 Deg. I had read on a web site that you should set to 29 rather than 30, there was a reason for it.

The Sandvick threading tool that I am using has an metal shim underneath the threading insert, I am sure this is to set the rake, I can only guess that the rake insert is negative, as the threading insert points down at the tip. I will go now and take a pic of the threading tool, to show rather than try explain.

Ian

The shim under the insert is not there to adjust rake. The shim is called an anvil and is used to adjust the helix angle of the insert. The most common helix angle anvil we would use on barrel threads is 1.5° and that angle anvil is what usually comes standard with the size toolholders we use. There should be some etched numbers/letters that will indicate what anvil it is and if you check the manufactures data for that toolholder/insert it will tell you what anvil you have. When looking at the insert face on (from the workpiece's perspective) you will notice the vertical portion of the cutting edge is not truly vertical but I would bet yours is 1.5°. Positive and negative anvils are also available so you can swap the toolholder positions, feed directions, left or right hand threads and keep the helix angle correct.

Your insert is not negative just because it is angled down. If you look at the actual cutting surface on top of the insert I think you will find it somewhat neutral to your workpiece. As in zero rake front to rear and side to side.

 

[p17p14enflield]

shim under insert

the shim's are available with 7 deffrrent rake angle on them !
buy some and trie them ! the down side to using insert type threading tooling is that no standred machine's the same rule dont work !

you can buy a set with all the shim's for you'r tool holder for £40 and it money well spent

 

[WSnyder]

If all you are doing is barrel work then the only anvil you will probably ever need is a positive anvil that will give you a 1.5° helix angle.

 

[papapaul]

It is suprising how much of the old industrial carbide tooling can only be run below center. I use an industrial thread cutter which has no releif angle, can only be run below center, and will not tolerate being advanced at 29 degrees when cutting. It will disintegrate. It will only cut being advanced straight in. But, having no relief angle the edge is better supported? Being industrial surplus, this stuff could be, probably is, for some specific application. Maybe particularly hard material, who knows.