PDA

View Full Version : Lesson in life and internal threads



mototed
07-16-2011, 02:17 PM
So, I got a stand up insert tool #2 size that uses the notched inserts. Going to cut a 1" x 12 tip internal blind thread 1.5" in 4140 steel. My second try at this after using a homemade "flexible" bar.
First cut , I run the bar in too far and hit the blind. Snaps top of insert off immediately. Opps! Well we will just flip it over and try to be more careful next time. Make about four or five passes, nice long curls just like peeling an apple. I better be careful, this is working too sweet, only two or three more passes left. What was that little "peek" sound I heard when returning to the bottom of the hole? Cra##p , Insert ruined. Glad I have a spare. Throw it in and wound up with a nice threaded hole that cost me $12.00 for the ruined insert. The Great Dane shop dog doesn't understand that I am upset with myself for blowing $12 bucks for one threaded hole. He's all happy and I'm all pissed.

An hour latter it dawns on me. A 1"x12 tap costs $100 dollars. One missed turn in the car (gas @ $4.00 a gallon) could cost $10 bucks. Cost to have someone else to to make this for me, at least $50-75 dollars in shop labor.
I don't fell so bad now, plus I learned a few things. Life is good again.

Ted

Black_Moons
07-16-2011, 02:31 PM
Heh. Iv found a few ways to avoid that...

For example, Get a boring tool that can be turned upside down, Or one that can cut on the back side of the bore, Then run the spindle in reverse.

You'll thread *out* of the blind hole insted of into it.

You can also set up a TDI, have it so that say its 1 or 2 revolutions before the 'end' of the blind hole (Should be a runout groove in there!), then you just keep an eye on it for when to open the half nut.

jkilroy
07-16-2011, 03:03 PM
Second what he said!! If possible I always cut a big relief at the bottom.and do exactly that, reverse and upside down, cut out of the hole.

macona
07-16-2011, 03:12 PM
Why did you have to thread so deep?

Forrest Addy
07-16-2011, 05:10 PM
Yeah, I prefer an indicator stop. You can see the carriage approach the indicator so when the dial starts winding down to zero you're not surprised. You have time to grip the half nut handle and the cross slide handle and when zero come you disengage and dial the tool away from the cut in one smooth unhurried motion. WHen you look the indicator hand is exactly on zero and the internal pull-out looks "factory".

You set the indicator by positioning the tool at the thread start. Set a block on the ways next to the carriage, crank the carriage down the hole to the thread depth as measured to the block or to the DRO if you are fortunate enough to have on on your lathe), set the indicator to the zero you prefer to work with.

A 0.001 graduated 2" dial indicator on a biscuit magnet works best for me. These indicators at rest read .025 before the first zero. I set the indicator to read the second zero where I want the threads to stop. I use 1.000" travel indicators for this. This makes a compact low profile arrangement easy to place and adjust and easy to store stuck in the side of your tool box. The stem is conveniently parallel to the back and about an inch off the way it's stuck to. They are inexpensive and so if you damage one it won't break he bank.

This kind of magnet: http://cgi.ebay.com/SPECIAL-PRICE-3pc-BRAND-NEW-INDICATOR-MAGNETIC-BACK-/120487438722?pt=LH_DefaultDomain_0&hash=item1c0d9c6982

And this kind of indicator: http://cgi.ebay.com/NEW-0-1-Travel-Dial-Indicator-Jeweled-001-Resolution-/220585527761?pt=LH_DefaultDomain_0&hash=item335bec09d1 This links to a cheap no-name indicator I'm using just to illustrate my point. Let quality be your guide.

Do NOT use a digital indicator or a zero on the DRO. People are analog critters. They respond instantly when a hand sweeps past a zero but are caught asleep at the switch every time they watch a digital display count down to zero.

Al Messer
07-16-2011, 05:29 PM
I vote with "Black Moons"---thread blind holes in reverse---no smashups with that method.

DATo
07-16-2011, 05:29 PM
I second everything Forrest Addy said. I've found the indicator stop the best way to stop short of bottoming out.

JCHannum
07-16-2011, 05:32 PM
When threading to a shoulder or in a blind hole, if you are using the compound set at 60*, remember that the tool bit is advancing with each pass. A hard stop or dial indicator will not account for this, and it is possible that you will foul on the shoulder or hole bottom if you rely on the position of the carriage.

When threading a blind hole, I usually make the hole deeper than the thread and allow the workpiece to make a couple of revolutions after disengaging the feed to create a relief.

mototed
07-16-2011, 05:40 PM
I did go left to right in reverse. I still managed to mess it up. Like I said, It's my first time for a internal blind thread. I have no machine shop experience. I learned a lesson today and it cost me $12 dollars. I was a little depressed over that, but after a while, hey no big deal. Next time I think that I will know better. I pretty much learned every thing I know off of this web site, so thanks for all the help.
Ted

DATo
07-16-2011, 06:15 PM
When threading to a shoulder or in a blind hole, if you are using the compound set at 60*, remember that the tool bit is advancing with each pass. A hard stop or dial indicator will not account for this, and it is possible that you will foul on the shoulder or hole bottom if you rely on the position of the carriage.

When threading a blind hole, I usually make the hole deeper than the thread and allow the workpiece to make a couple of revolutions after disengaging the feed to create a relief.


That's a great point and one I failed to mention. You were quite right to point it out ... thanks !

With each advance of the compound you are moving your stop point deeper and deeper into the hole. In my case I feed 90 degrees on the cross feed rather than the normal 29 on the compound for most of the thread depth. I then clean up on the last couple of cuts using the compound. Those last few cuts don't advance the tool enough to bottom out.

beanbag
07-16-2011, 06:19 PM
Stop the motor before you reach the end and then turn the chuck by hand.

Teenage_Machinist
07-18-2011, 01:56 AM
I have a carbon steel internal threading bar, and will not have that problem...

Allan Waterfall
07-18-2011, 02:27 AM
..

For example, Get a boring tool that can be turned upside down, Or one that can cut on the back side of the bore, Then run the spindle in reverse.


I can never understand why people think because you're cutting in the back of the bore you need to run the lathe in reverse.
If you turn the tool upside down and reverse the lathe it's the same as trying to bore with the bit at the front with the lathe in reverse...it doesn't work.

Just flip the boring bar over and use the lathe in the normal direction.Swarf drops off the bit into the bottom of the bore and it's easier to see progress.

Allan

franco
07-18-2011, 09:47 PM
I can never understand why people think because you're cutting in the back of the bore you need to run the lathe in reverse.
If you turn the tool upside down and reverse the lathe it's the same as trying to bore with the bit at the front with the lathe in reverse...it doesn't work.

Just flip the boring bar over and use the lathe in the normal direction.Swarf drops off the bit into the bottom of the bore and it's easier to see progress.

Allan
Allan,

The reason for running the spindle backwards when threading a blind hole is that you avoid any danger of running the boring bar into the blind end of the hole, because you are cutting towards the tailstock.

franco

adatesman
07-18-2011, 11:58 PM
Can't offer advice that wasn't given above, so will instead request pics of the pup. Lost our Great Dane Shop Dog a couple months back (to Wobbler's) and the shop's just not the same without her. :-(

Allan Waterfall
07-19-2011, 05:09 AM
Allan,

The reason for running the spindle backwards when threading a blind hole is that you avoid any danger of running the boring bar into the blind end of the hole, because you are cutting towards the tailstock.

franco
Yes,but what I'm saying is if you flip the tool over and try to cut at the back with the lathe in reverse the tool will not cut.

Allan

Black_Moons
07-19-2011, 05:49 AM
I never said flip the toolbit AND put it at the back of the bore AND run in reverse.

I said (flip the toolbit upside down *OR* put it at the back of the bore) AND run in reverse.

Either way allows the toolbit the correct orientation to run with the spindle in reverse. Technicaly its better to put down force (Back of the bore) on the lathe then up force (toolbit upside down) Since lathes don't allways have much holding down the carriage besides weight.

Upside down *AND* back of bore (or behind work for OD turning) = upward force and cuts in forward of course. Used primarly for rear toolpost cutoff tools. (Better chip evacuation for cutoff. rigid and conviant due to deticated, compoundless toolpost that never needs realigning).

Richard Wilson
07-19-2011, 06:20 AM
I never said flip the toolbit AND put it at the back of the bore AND run in reverse.

I said (flip the toolbit upside down *OR* put it at the back of the bore) AND run in reverse.

Either way allows the toolbit the correct orientation to run with the spindle in reverse. Technicaly its better to put down force (Back of the bore) on the lathe then up force (toolbit upside down) Since lathes don't allways have much holding down the carriage besides weight.

Upside down *AND* back of bore (or behind work for OD turning) = upward force and cuts in forward of course. Used primarly for rear toolpost cutoff tools. (Better chip evacuation for cutoff. rigid and conviant due to deticated, compoundless toolpost that never needs realigning).

Umm - if you flip the tool and cut from the blind end outwards to avoid the risk of running into the blind end, which is where the discussion was going, then you cut a left hand thread. Tool at the back, spindle in reverse, cutting from the blind end out, thats a right hand thread, but you can't do that with a standard internal threading tool, the insert faces the wrong way. or are some of them reversible?

I try to provide a blind end recess about 2 full threads long, and major diameter of the recess about .010" larger than the OD of the thread. Soon as the cutting sounds stop, knock out the half nuts. Works for me.

richard

Black_Moons
07-19-2011, 07:11 AM
Umm - if you flip the tool and cut from the blind end outwards to avoid the risk of running into the blind end, which is where the discussion was going, then you cut a left hand thread. Tool at the back, spindle in reverse, cutting from the blind end out, thats a right hand thread, but you can't do that with a standard internal threading tool, the insert faces the wrong way. or are some of them reversible?

I try to provide a blind end recess about 2 full threads long, and major diameter of the recess about .010" larger than the OD of the thread. Soon as the cutting sounds stop, knock out the half nuts. Works for me.

richard

Nope, Upside down tool requires the spindle run in reverse, Hence, cutting away from the headstock produces a right hand thread.

Upside down tool = Tool at back, Exact same result, just diffrent position of the tool.

I don't know about standard internal threading tools, I use a HSS bit I ground myself in a standard boring bar.

PS: REAL fun starts when you cut metric threads on an imperial lathe, And can not open the half nut.
With no VFD, it can take more then 2 revolutions easy for a large lathe to come to a stop, even at the lowest speeds.

Richard Wilson
07-19-2011, 09:54 AM
Nope, Upside down tool requires the spindle run in reverse, Hence, cutting away from the headstock produces a right hand thread.

Upside down tool = Tool at back, Exact same result, just diffrent position of the tool.

I don't know about standard internal threading tools, I use a HSS bit I ground myself in a standard boring bar.

PS: REAL fun starts when you cut metric threads on an imperial lathe, And can not open the half nut.
With no VFD, it can take more then 2 revolutions easy for a large lathe to come to a stop, even at the lowest speeds.


Yes you are right - my misunderstanding.

Richard

steverice
07-19-2011, 12:16 PM
I like to run my lathe in reverse with a tool that was ground for running on the back side of the turning when I do an internal thread up to a step, it does help me keep from running the tool into the works step, but then I am just a hack working in my garage.

Black_Moons
07-19-2011, 01:21 PM
Yes you are right - my misunderstanding.

Richard

For extra fun, I once did thread upside down away from a 0.1" shoulder in aluminum with a 1/2" HSS threading bit I made.... And accidently put it in forward....

It *displaced* 3 turns or so of thread into the shoulder before I turned the lathe off. OD was much bigger then it started. Root of threads looked good. Crest was uber nasty since at that depth it was displacing much deeper then a thread depth.

So, it kinda works either way :)