# Is This Lathe Tool Bit Okay?



## devils4ever (Apr 3, 2021)

I'm working on a project where I need to do an internal blind 1-8 thread in steel on my lathe. So, I decided to get a left-hand threading tool so I can thread away from the headstock. I searched and found the Micro 100 one would work. I ordered one from Amazon, but after weeks they decided they couldn't get it. So, I found one on eBay in "New-open box" condition. I ordered it and it arrived with a small nick/chip taken out of the top surface. See photo. I'm not sure this will affect the performance since I'll be threading at 29.5 degrees on the right side of the bit. So, what does everyone think? Is this okay? Should I return it? I did have a hard time finding this bit and it was half the price of Amazon. Thanks!


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## savarin (Apr 3, 2021)

Is the tip still sharp?
If so then there looks to be sufficient material to cut a pretty deep thread.
I would go for it but I dont know what a 1-8 thread is.


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## devils4ever (Apr 3, 2021)

It seems sharp, but I'm not ready to use it quite yet to try it.

1-8 thread is 1" in diameter and 8 TPI which is about a M25.4X3.175 or the closest equivalent is M24X3.


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## savarin (Apr 3, 2021)

So is there still sufficient material to fully form the complete flanks of the thread?
It looks as if there is but just check it.


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## devils4ever (Apr 3, 2021)

I believe so, but for a really deep thread, the chipped area _may _come into play.


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## SLK001 (Apr 3, 2021)

It will be okay (for what you plan on doing).  The right side will be doing all the cutting, so the left side won't come into play.  You don't say how big the bit is, so if you want to use the bit for an external thread, the thread flank length has to be shorter than the good area on the bit.

Is the bit carbide, or HSS?  Any theories on how the bit got chipped?


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## T Bredehoft (Apr 3, 2021)

It appears that  both sides of the point are chipped. a view from the top would answer lots of questions. 

If both sides are chipped, resharpening (remove enough of the top to remove the chips) is in order. This will maintain the correct profile.


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## BladesIIB (Apr 3, 2021)

The picture is a little fuzzy, it almost looks like the wax coating is what is chipped on the left side and at the tip? Has that yellowish color and seems to be scraped away a bit in the bottom left corner as well?  I would think you could sharpen it as needed to remove any true chips in it and be able to use it.


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## mickri (Apr 3, 2021)

What's the reason that you need to thread in reverse to thread a blind hole?  I am a rank beginner at machining and I have had no problems threading a blind hole.  Cut a thread relief (wrong term??) at the bottom of the hole and thread in the normal manner.  I have even done it without a thread relief.  Set up a carriage stop and disengage the half nuts as the carriage just kisses the stop.  I use a piece of paper to determine when to disengage the half nuts.  Wiggle the paper back and worth as the carriage approaches the stop.  When you can't move the paper disengage the half nuts.  After you have disengaged the half nuts there is no rush to back off the tool bit and pull it out of the hole.  It's not going anywhere. I use this same technique to bore a blind hole.


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## devils4ever (Apr 3, 2021)

It's solid carbide. I think just the top on the left side is damaged. I don't think there's any wax on it. I only have a diamond "file" for sharpening. I'm not sure this work taking a lot of material off.

I'll see if I can get a better picture.

I threaded the external threads for this already and it was exciting since the thread pitch (8 TPI) is so fast. With my mini-lathe, as soon as the tool gets to the relief cut, it speeds up dramatically. For a blind hole, this would cause a crash at the bottom of the hole. Watch some Joe Pi YT videos, he always threads away from the headstock. I can't do this easily for external threads, but I can for internal threads.


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## MrWhoopee (Apr 3, 2021)

mickri said:


> What's the reason that you need to thread in reverse to thread a blind hole?  I am a rank beginner at machining and I have had no problems threading a blind hole.  Cut a thread relief (wrong term??) at the bottom of the hole and thread in the normal manner.  I have even done it without a thread relief.  Set up a carriage stop and disengage the half nuts as the carriage just kisses the stop.  I use a piece of paper to determine when to disengage the half nuts.  Wiggle the paper back and worth as the carriage approaches the stop.  When you can't move the paper disengage the half nuts.  After you have disengaged the half nuts there is no rush to back off the tool bit and pull it out of the hole.  It's not going anywhere. I use this same technique to bore a blind hole.
> 
> View attachment 361573



You sound pretty experienced for a rank beginner. In a similar fashion, I just zero the DRO at the bottom of the hole and disengage 10 or 20 thou before the bottom. In the OP's situation, at 8 TPI things are moving pretty fast even at low speeds.


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## devils4ever (Apr 3, 2021)

You can say that again. Every revolution is 125 thou!

My mini lathe struggles to do the cut because of the fast speed and the deep cut. As it enters the relief groove, it jumps forward as the bit clears! Very exciting!!!


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## mickri (Apr 3, 2021)

My lathe runs at 28 rpm when threading.  The thing I practiced the most on when I first started was threading.  Just learning the repetitive hand movements.  I probably spent 8, maybe 10 hours over a week or so practicing on pvc pipe.  I also had the drive belts really loose so if anything went awry the spindle would stop instead of causing damage.  Even with this practice sometimes my threads don't come out right.  Usually when I try a different way to thread.  I have graduated from being a clueless newbie to being a rank beginner.  I have lots to learn.


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## devils4ever (Apr 4, 2021)

Here's a better shot.


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## mikey (Apr 4, 2021)

Micro 100 carbide is not like the typical solid carbide other makers use. It is tougher somehow. If you drop a typical carbide tool on a concrete floor it will likely shatter but a Micro 100 tool will usually not. I don't know what the metallurgical difference is but they make really good tools. With that said, that chip is one hell of a stress riser and a threading tool is under tremendous stress. I do not know if the tool will break in use but if it does, it will break at that chip.

If it possible to return it for an intact one then I would do that. If it is not possible then it might be possible for Micro 100 to regrind it for you to eliminate the chip. If they will not do that then you or perhaps someone on the forum can try to grind the top flat to eliminate the chip.


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## devils4ever (Apr 4, 2021)

Like I mentioned, this was bought on eBay in "New-open box" condition. So, I was expecting it to be perfect. However, I was thinking of using it "as is", not thinking that the chip could be a stress riser. 

I can contact the seller and see what he can do although this was the only one he had. Probably a refund would be the only recourse.


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## mikey (Apr 4, 2021)

Hopefully he will refund you and let you keep it. Then you can try it and if it breaks then you can look for another one.


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## BladesIIB (Apr 4, 2021)

devils4ever said:


> Here's a better shot.
> 
> View attachment 361646


Looking at that new pic, the tip seems to be chipped off.  Still looks like you can sharpen and will need to sharpen before using.


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## Janderso (Apr 4, 2021)

One way to find out.
10 hours of practice on pvc?
Boy, I wish I had your patience.


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## savarin (Apr 4, 2021)

The tip looks as if its crumbled so def needs a sharpen but after that I reckon its good to go, the chip just looks like a flake has popped off, can you grind the flat surface down to below the chip.


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## Papa Charlie (Apr 4, 2021)

The tip as mentioned is not sharp, looks like it has gone through the mill. That tool is in no way "Like New Condition". I would return it and get another from a reputable company.


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## Winegrower (Apr 4, 2021)

MrWhoopee said:


> mickri said:
> 
> 
> > What's the reason that you need to thread in reverse to thread a blind hole? I am a rank beginner at machining and I have had no problems threading a blind hole. Cut a thread relief (wrong term??) at the bottom of the hole and thread in the normal manner. I have even done it without a thread relief. Set up a carriage stop and disengage the half nuts as the carriage just kisses the stop. I use a piece of paper to determine when to disengage the half nuts. Wiggle the paper back and worth as the carriage approaches the stop. When you can't move the paper disengage the half nuts. After you have disengaged the half nuts there is no rush to back off the tool bit and pull it out of the hole. It's not going anywhere. I use this same technique to bore a blind hole.
> ...



This is interesting.   My first thought is that Mickri, you have the reflexes of a cheetah.    For example, even cutting at 28 rpm, and say, a 20 tpi thread, you are advancing 0.050 in two seconds.   If you are using a 3 thousandth paper, that gives you 2 *(.003/.050) seconds to react and disconnect.   This is 0.12 seconds.   Impressive!

But for me, 28 rpm would be way too slow to get good cutting action.   I like about 10X that, which if you are threading away from the headstock is easy, and does not require your lightning reflexes.    Joe Pie had a video about this, threading at turning speed...zip, the thread pass is done.


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## nnam (Apr 4, 2021)

Threading away is a great idea.  It would be for left hand thread, unless rumming backward and does that mean the cutter has to point the other way?


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## mickri (Apr 4, 2021)

It doesn't seem like I am having to make a fast reaction to disengage the half nuts.  I feel the paper start to catch with my left hand and my right hand flips up the half nut lever.  Sure it only takes a fraction of a second to do that.  It just seems natural and no big deal.

It seems like everybody is trying to see how fast they can do things.  In a production shop where time is money you have to work as quickly as possible.  On the other hand we hobby guys have all the time in the world.  So running at slower speeds is no big deal.  I would bail on this hobby in a heart beat if running the machines stressed me out.  I do this for fun  I left the pressure cooker job a long time ago and have never looked back.


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## devils4ever (Apr 4, 2021)

I asked the seller for replacement or refund. Maybe, he'll tell me to keep it and I'll try using it.

Since it's carbide, I don't have a way to grind this. I assume you need diamond?

The spindle runs backwards for this operation and away from the headstock. This still cuts a right hand thread, but the cutter is engaging the work on the back side of the hole. The tool bit has its cutting edge on the opposite side of a standard tool bit.


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## BladesIIB (Apr 4, 2021)

devils4ever said:


> I asked the seller for replacement or refund. Maybe, he'll tell me to keep it and I'll try using it.
> 
> Since it's carbide, I don't have a way to grind this. I assume you need diamond?
> 
> The spindle runs backwards for this operation and away from the headstock. This still cuts a right hand thread, but the cutter is engaging the work on the back side of the hole. The tool bit has its cutting edge on the opposite side of a standard tool bit.


You don’t have to have diamond. A green silicon carbide wheel works fine. Diamond is nice to finish it after but not required.


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## hman (Apr 4, 2021)

nnam said:


> Threading away is a great idea.  It would be for left hand thread, unless rumming backward and does that mean the cutter has to point the other way?


I'm not sure if I understood your question correctly, but here's a quick rule of thumb:
If the spindle and leadscrew are both rotating in the same direction, it will be a right-hand thread, regardless of tool location or spindle rotation direction.  Left-hand threads are obtained when the spindle and leadscrew rotate in opposite directions.


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## nnam (Apr 4, 2021)

devils4ever said:


> I asked the seller for replacement or refund. Maybe, he'll tell me to keep it and I'll try using it.
> 
> Since it's carbide, I don't have a way to grind this. I assume you need diamond?
> 
> The spindle runs backwards for this operation and away from the headstock. This still cuts a right hand thread, but the cutter is engaging the work on the back side of the hole. The tool bit has its cutting edge on the opposite side of a standard tool bit.


That's what I thought also.  Your tool looks like it's pointing down if cutting on the front of the lathe (pointing at an operator), unless the camera flipped it, but you already confirmed the tool is pointing the opposite of regular inside thread tool does.


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## nnam (Apr 4, 2021)

hman said:


> I'm not sure if I understood your question correctly, but here's a quick rule of thumb:
> If the spindle and leadscrew are both rotating in the same direction, it will be a right-hand thread, regardless of tool location or spindle rotation direction.  Left-hand threads are obtained when the spindle and leadscrew rotate in opposite directions.


If the tool is for inside thread (female), and it points toward the operator, and if the chuck rotates backward (reversed), then the tool needs to face down.  To mount that tool facing up, it would cut facing away from the operator for a reversed rotating chuck.


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## mmcmdl (Apr 5, 2021)

Need a better pic to see exactly what you have there . I have Kennemetal Top Knotch bars in both hands if you need them .


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## Papa Charlie (Apr 5, 2021)

nnam said:


> If the tool is for inside thread (female), and it points toward the operator, and if the chuck rotates backward (reversed), then the tool needs to face down.  To mount that tool facing up, it would cut facing away from the operator for a reversed rotating chuck.



Here is the sequences for Right and and Left hand internal threads both feeding towards and away from the head stock

For standard Internal Right Hand threads normal feed:
1) The chuck turns CCW as normal. 
2) The tool will face the operator with the cutting face up
3) The carriage will travel towards the head stock

For standard internal Right Hand Threads reverse feed:
1) The chuck turns CW reverse of normal
2) The tool will face away from the operator with the cutting face up.
3) The carriage will travel away from the head stock

For Left Hand Threads normal feed:
1) The chuck turns CW reverse of normal
2) The tool will face away from the operator with the cutting face up.
3) The carriage will travel towards the head stock

For Left Hand Threads reverse feed:
1) The chuck turn CCW as normal
2) The tool will face the operator with the cutting face up
3) The carriage will travel away from the head stock


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## devils4ever (Apr 5, 2021)

There seems to be a lot of discussion and confusion on cutting an internal, blind, right-hand thread with a left-hand lathe bit. Just watch Joe Pi's video and all will be made clear!


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## macardoso (Apr 5, 2021)

nnam said:


> Threading away is a great idea. It would be for left hand thread, unless rumming backward and does that mean the cutter has to point the other way?


I bought a few left hand internal threading tools for exactly this reason. Insert facing up, cutting on the backside of the bore, spindle running backwards, threading away from the chuck. Yes it is an operation specific tool, but often the right tool for the job.


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## mmcmdl (Apr 5, 2021)

The reason I have them is some cnc lathes require them , and I ran quite a few in the past .


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## nnam (Apr 5, 2021)

Thank you for the detailed write up, hope you don't mind I insert some more below. 
Please correct me if  I'm wrong.  Summary for internal thread:

CW and away head or CCW and toward head: right hand thread, otherwise left hand

CW: face down toward oper, or face up away from oper.
CCW: face up toward oper., or face down away from oper.




Papa Charlie said:


> Here is the sequences for Right and and Left hand internal threads both feeding towards and away from the head stock
> 
> For standard Internal Right Hand threads normal feed:
> 1) The chuck turns CCW as normal.
> ...


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## macardoso (Apr 5, 2021)

nnam said:


> Thank you for the detailed write up, hope you don't mind I insert some more below.
> Please correct me if  I'm wrong.  Summary for internal thread:
> 
> CW and away head or CCW and toward head: right hand thread, otherwise left hand
> ...


Sounds right to me. Either way (right side up, back side of bore, or upside down, operator side of bore) if you are threading away from the chuck for a RH thread, you will need a LH threading tool. 

I found this all very confusing when I asked this question for the first time, but after you try it once, it will make sense.

Sample cut, 1"-20tpi (arbitrary) internal thread against a shoulder. I *personally* would use a 1/2" indexable LH threading tool, right side up, cutting on the back side of the bore, away from the chuck, with the tumbler gears set to normal "forward" direction.


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## devils4ever (Apr 6, 2021)

Update: The seller refunded me my money. I went ahead a bought one from Travers.


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## devils4ever (Apr 7, 2021)

The seller isn't asking me to return this. Maybe, I can sharpen it in the future when I can grind carbide.


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## devils4ever (Apr 14, 2021)

New one from Travers has arrived. Much, much better!


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