Another Question on Threading and Methodology

[Bully]

So, I've cut a couple of threads. I'm certainly no expert, but I do understand the concepts fairly well. That said, I know that folks will debate the 29.5* compound angle vs. the 30* compound angle for single point thread cutting until the end of time. And that's all well and good. However I recently watched a video by a fairly well respected 'smith on chambering and threading and his compound was set at 90*. I'm wondering if anyone can explain it and if/why it may work for him but not be recommended. I do believe he is using a carbide insert/full profile tool, which may be part of it and not something I'm at all familiar with.

I'm hoping we can all avoid a pissing match. I'm simply looking for information and hope we can all respect each other's methods.

Thanks in advance.

 

[GenePoole]

I posted this in a thread a while back. I hope it sheds some light on the subject. Some compounds have different scales and 90° can mean either parallel or perpendicular to the workpiece. If 90° to the workpiece, then it's the same as doing a straight-in plunge cut with the cross-slide. If 90° relates to the angle between the cross-slide and compound, then this can be a technique for picking up an existing thread.

http://forum.accurateshooter.com/th...ned-12-30-update.3940291/page-8#post-37114237

 

[Bully]

@GenePoole , thank you for the response.

The compound is set perpendicular to the work. Like a "T" if you will. He was pushing the tool straight into the work. It was a fresh, outside thread.

 

[ridgeway]

You can certainly feed the cross feed in at 90 degrees for each pass. It's how CNC usually thread.

 

[Cloudrepair]

I like both methods but almost always do it with my compound at a parrallel 90* for picking up threads again if i need to.
Just like 90* better i guess but there is more chance of chatter/harmonics that way.

 

[Steve morgan]

You can certainly feed the cross feed in at 90 degrees for each pass. It's how CNC usually thread.

When you feed streight in you cut on both sides of the insert,when you feed in at29.5 you cut on 1 side

 

[Dusty Stevens]

Just because its on youtube doesnt make it right either. Youll never know the difference between 29.5 and 30 on the threads we cut and probably wont notice it set at 90. Its when you cut the 32+ tpi you better be on your game. Its very easy to test both ways

 

[ridgeway]

When you feed streight in you cut on both sides of the insert,when you feed in at29.5 you cut on 1 side

Yep, cuts on both sides. I feed in at 29.5. When getting close to depth, will clean up feeding in on cross feed a few thou. I use a simple 60 degree carbide insert. If one chooses to use full profile inserts...probably best to feed everything in with crossfeed.

 

[Bully]

Just because its on youtube doesnt make it right either. Youll never know the difference between 29.5 and 30 on the threads we cut and probably wont notice it set at 90. Its when you cut the 32+ tpi you better be on your game. Its very easy to test both ways

Thank you for taking the time to respond. The video was not on YouTube. Nor did I say it was right. I'm looking for reasons for the methodology. Not really anything more. In my developmental stage I am looking for all the methods I can find and then I will distill them down to what works for me.

 

[Dusty Stevens]

very few gunsmiths are actually machinists. some have taken machining classes but most have learned from a mentor or whatever then took that and mixed with their own methods to come up with the end result they deem acceptable. like I said its easy enough at this stage in your game to try both ways. like ridgeway said above setting your compound at 29.5 it cuts on one side of the thread and 90 it cuts on both. I cut at 29.5 except for maybe a couple thousandths for cleanup. I've never seen anybody set their compound at 90deg to thread but thats not saying it wont work. that old book by south bend called how to run a lathe may be a good addition to your collection. everybody should read thru it as they begin machining

 

[Bully]

very few gunsmiths are actually machinists. some have taken machining classes but most have learned from a mentor or whatever then took that and mixed with their own methods to come up with the end result they deem acceptable. like I said its easy enough at this stage in your game to try both ways. like ridgeway said above setting your compound at 29.5 it cuts on one side of the thread and 90 it cuts on both. I cut at 29.5 except for maybe a couple thousandths for cleanup. I've never seen anybody set their compound at 90deg to thread but thats not saying it wont work. that old book by south bend called how to run a lathe may be a good addition to your collection. everybody should read thru it as they begin machining

Thank you. I actually have it and have skimmed it. I'll give it a more in-depth look today since the weather in my part of the world is atrocious.

 

[Intheshop]

IME,the problems with coming in at a 90 is chips getting wedged in and the need for perfect tool geometry.

 

[Steve morgan]

Yep, cuts on both sides. I feed in at 29.5. When getting close to depth, will clean up feeding in on cross feed a few thou. I use a simple 60 degree carbide insert. If one chooses to use full profile inserts...probably best to feed everything in with crossfeed.

When you.feed straight in you have to really watch your in feed,depth of cut- to much and your threads will look like you cut them with a chisel

 

[TAJ45]

IME,the problems with coming in at a 90 is chips getting wedged in and the need for perfect tool geometry.

 

[TAJ45]

A 90° plunge will give a lot of friction/heat. The CNC plus is with rigidty and coolant flooding. That method allows for back rake but no side rake tool geometry.
I have on occasion plunged for abt 50% of thread depth then gone back in @ 29.5° picking up with a slick HS tool to finish out. The lower rpm for HS allows a bit more time to pull, requires much less pressure to cut than carbide and easier to shave /skim cut. Carbide needs pressure to work = push off. These characteristics are especially prevalent when manual machining.

 

[Bully]

A 90° plunge will give a lot of friction/heat. The CNC plus is with rigidty and coolant flooding. That method allows for back rake but no side rake tool geometry.
I have on occasion plunged for abt 50% of thread depth then gone back in @ 29.5° picking up with a slick HS tool to finish out. The lower rpm for HS allows a bit more time to pull, requires much less pressure to cut than carbide and easier to shave /skim cut. Carbide needs pressure to work = push off. These characteristics are especially prevalent when manual machining.

Thank you.
I am running a HSS cutter from AR Warner. Not running carbide at this time. No plans to in the foreseeable future. From what I can tell, the HSS will work best for me.