# Threading Question.



## Fldvr (Apr 9, 2015)

Hi everyone, I've done a little threading on non critical parts using the cross slide.  Now
  that I'm ready to move on to the compound I find myself wondering about the depth of cut.
When using the cross slide and  I wanted to make a thread with say a depth of .100 then I would
gradually move the cross slide in until I had a total of .100

Now my question is, when using the compound there must be some difference in the depth of
cut due to the angle/movement of the slide.  Is there a correction factor that seems to be eluding me
here? I have read and looked on you tube but do not see any references.


----------



## Bamban (Apr 9, 2015)

The movement is the sine of whatever angle you have the compound set. At 30 degrees (assuming it is exactly 30 degrees) the movement is 0.5 for every compound increment. For all practical purposes, assume the .5 movement. I am a total newbie myself, and I experiment with different ways to get the job done. On threading I stick a dial indicator on the tool post with the mag base on the saddle, square it and level it and I just use it to measure the cut since I normally use the cross slide for the last couple of thou.

I may be out of my league here, the pros can chime in and correct me please.


----------



## T Bredehoft (Apr 9, 2015)

Professionally, I've never concerned myself with Depth of Cut while threading, other than individual cuts. There are thread mikes or PD Thread wires to tell you when you're deep enough. Anything else is guesswork.

I always use the compound for increment the cut, the cross slide is for backing out at the end and returning to datum before starting the next pass


----------



## Ken_Shea (Apr 9, 2015)

My thread specification software shows the compound infeed amount.
Beyond that , in my very unprofessional guesswork  is to use the nut I am going to use to check fit when it gets close.

Just being practical TB, you are of course correct in all that you say but most hobby machinist do not have thread mikes or thread wires.

Ken


----------



## Wreck™Wreck (Apr 9, 2015)

T Bredehoft said:


> Professionally, I've never concerned myself with Depth of Cut while threading, other than individual cuts. There are thread mikes or PD Thread wires to tell you when you're deep enough. Anything else is guesswork.
> 
> I always use the compound for increment the cut, the cross slide is for backing out at the end and returning to datum before starting the next pass


*What he said!!!*
Turn close, measure, turn finish pass to desired size (repeat as needed), all of the folklore, how to guides, text books, rules of thumb and downright misinformation will only get you close. If you are a hobbyist buy a thread wire set and learn to use it, as unpleasant as that is. I do this for a living and use wires when we don't have any other way to measure a particular thread, very accurate in skilled hands yet cumbersome to use at best.
Good Luck


----------



## randyc (Apr 9, 2015)

Ken_Shea said:


> ... most hobby machinist do not have thread mikes or thread wires.  Ken



Ken, you're probably right about thread micrometers and maybe even regarding thread wires but there's really NO reason for not owning a set of thread wires ($7 from CDCO, for example).  Takes a little practice to use the wires but _some_ pitch diameter measurement capability beats _none_, right ?


----------



## Wreck™Wreck (Apr 9, 2015)

randyc said:


> Ken, you're probably right about thread micrometers and maybe even regarding thread wires but there's really NO reason for not owning a set of thread wires ($7 from CDCO, for example).  Takes a little practice to use the wires but _some_ pitch diameter measurement capability beats _none_, right ?


Measurement over wires is extremely accurate, think of it as a sine bar for compound angles.

I did a thread 2 weeks ago that isn't even listed in MH, 2 15/16-8 X 5 LH (the left handedness is meaningless since it measures the same) fortunately the Customer had a sample that I could measure over wires because it had to fit an existing component of unknown age and condition. Hasn't come back yet but time will tell.


----------



## Ken_Shea (Apr 9, 2015)

If a particular class fit was required then I'd be all over a set of thread mikes and wires, when it's not you just do not need them and a good thread job would be done by the time I was done finding, selecting and fiddling around with a set of thread wires.

Don't take me wrong, and I certainly made no argument against the proper method/s nor would even the thought of suggesting other wise cross my mind to one who wanted to use/learn them. That said, in 50 + on/off years of hobby machining I've managed well with out either and I do not put out junk sloppy jobs. Professionally, that senario would be a much different.

Ken


----------



## randyc (Apr 9, 2015)

Wreck™Wreck said:


> Measurement over wires is extremely accurate, think of it as a sine bar for compound angles...



I agree and used wires + masking tape for years.  I have a hereditary motor movement problem that causes severe tremors in both hands (it has gotten worse as I age).  After dropping a wire three times before getting a measurement, I gave up and got thread micrometers


----------



## Ken_Shea (Apr 9, 2015)

Wreck™Wreck said:


> I did a thread 2 weeks ago that isn't even listed in MH, 2 15/16-8 X 5 LH



That is a very good example of needing/using them that I hadn't thought of.


----------



## Ken_Shea (Apr 9, 2015)

randyc said:


> got thread micrometers



Priced them once, sticker shock


----------



## randyc (Apr 9, 2015)

Ken_Shea said:


> ...That said, in 50 + on/off years of hobby machining I've managed well with out either and I do not put out junk sloppy jobs...



Can't argue with success, peace, brother  ($79 for one inch thread micrometers, BTW.)


----------



## Wreck™Wreck (Apr 9, 2015)

randyc said:


> I agree and used wires + masking tape for years.  I have a hereditary motor movement problem that causes severe tremors in both hands (it has gotten worse as I age).  After dropping a wire three times before getting a measurement, I gave up and got thread micrometers


Sorry to hear that, I generally do largish work yet I still put a plastic tray across the ways with a clean rag in it under the part to be measured and still set free the occasional wire into the soup, fortunately large wires are relatively easy to find.


----------



## Tony Wells (Apr 9, 2015)

Randy, just food for thought, but there is a way to use a single wire. Just measure the actual major diameter and do a little math. Handling one wire is much easier than 3.


----------



## randyc (Apr 9, 2015)

Wreck™Wreck said:


> ... I still put a plastic tray across the ways with a clean rag in it under the part to be measured and still set free the occasional wire into the soup...



I followed a similar practice: laying a white rag across the ways, held in place with a couple of magnets.  But I sometimes even have problems typing, LOL, so thread mikes are now a necessity rather than just a convenience 

_(My own tremors are troublesome but my youngest sister, who has the same disease as me, makes her living designing and producing one-off custom jewelry.  This is career ending as her tremors worsen.)_


----------



## 18w (Apr 9, 2015)

I have used modeling clay to stick those pesky buggars in place. I also have a set of thread triangles that have rubber retainer bands that fit over the micrometer spindle faces. Both can be aggravating at times. 

Darrell


----------



## randyc (Apr 9, 2015)

Tony Wells said:


> Randy, just food for thought, but there is a way to use a single wire. Just measure the actual major diameter and do a little math. Handling one wire is much easier than 3.



Tony, I don't think that I'd trust that method for precise measurements.  You wouldn't be measuring the pitch diameter directly, you'd be measuring something like the differences in OD and PD.  (The 3-wire method doesn't measure pitch diameter directly either but it's much closer and doesn't depend on the loose tolerances of the OD.)

Let's pick a thread as an example, say 5/16-18UNC-3A where tolerances are as follows:

O.D.  .3038 to .3125 or a permissible variation of .0087
P.D.  .2734 to .2764 or a permissible variation of only .0030

Since the O.D. can vary by almost .009 and still be within UNC-3B tolerances, it seems to me that a pitch diameter measurement based on the O.D. might measure/calculate to be within specification but in fact be considerably out of tolerance.

I sincerely appreciate your suggestion since it was clearly intended to alleviate my motor skill problems   Thank you !


----------



## randyc (Apr 9, 2015)

Tony Wells said:


> Randy, just food for thought, but there is a way to use a single wire. Just measure the actual major diameter and do a little math. Handling one wire is much easier than 3.



Tony, I completely misunderstood the above.  You intended the single wire method to be made using measured OD, duh, not the limits of the thread tolerances.  Dunno where my mind was but I apologize for the gross misconception and I'm going to look into that technique a little closer.  Thank you again !


----------



## Tony Wells (Apr 9, 2015)

That's ok Randy. I had to demonstrate it more than a few time before I convinced a few people that it was adequate. I don't use that method for making or checking plug gages, but for product, it seems perfectly acceptable. It works.


----------



## RVJimD (Apr 11, 2015)

I may have missed it but, is there anything wrong with using a nut if you have one the correct size and TPI to check?  

Jim


----------



## Billh50 (Apr 11, 2015)

I usually use a nut unless I am looking for a very close fit for something that needs to be very accurate.


----------



## T Bredehoft (Apr 11, 2015)

_ is there anything wrong with using a nut?_

No, but you have to live with the tolerances of that particular nut.

The last time I made threads, I made a 1" x 10 to emulate the thread on my lathe spindle, checked both and found the spindle .012 under size.  I was making an ER40 adapter and wanted a good fit on the spindle. 

Tom


----------



## British Steel (Apr 11, 2015)

Talk of thread wires reminds me - I poke 'em into a wine cork at roughly the right spacing. Any excuse to open another bottle 

Dave H. (the other one)


----------



## Bill C. (Apr 11, 2015)

I personally don't recall using wires.  I know how to but never did.  I've used pitch gages and Go/No Go thread gages.  I can see using wires when rebuilding machines where a custom thread fit is required.  

I saw a YouTube video the other day of a CNC machinist/programer demonstrating a threading sub-routine.  He used a standard off the shelf nut to test the finished thread.  My old bosses would have fainted.  
I just love technology when it works.  Hope your day is a good one.


----------



## Wreck™Wreck (Apr 11, 2015)

RVJimD said:


> I may have missed it but, is there anything wrong with using a nut if you have one the correct size and TPI to check?
> 
> Jim


Yes, you are assuming a nut is a reliable gauge of PD.


----------



## Billh50 (Apr 11, 2015)

As I stated earlier. A nut is fine if you do not need the PD to be a close fit. If you are making something where the fit needs to have almost no slop or backlash then you would need either a gauge or pins to check PD.


----------



## Bill C. (Apr 11, 2015)

I would use a hexagon threading die sometimes when I am almost down the finished dimension.  By-the-way some of the round dies are adjustable, there will be a setscrew, so you can adjust the fit a little.

Standard nuts are slightly oversized.  Probably for the plating.


----------



## pdentrem (Apr 11, 2015)

One can also use home made wires. I used 3 carbide drill blanks to measure the PD on my lathe spindle when I made a couple backing plates for the lathe.
Pierre


----------



## JR49 (Apr 11, 2015)

RVJimD said:


> I may have missed it but, is there anything wrong with using a nut if you have one the correct size and TPI to check?
> 
> Jim


No Jim, using a nut, or whatever you have with known threads that are the same as you are cutting is fine. However it is good to know these measuring methods that the other guys are referring to for the time when you are asked to make a part with threads to mate to a part that you don't have access to.  Then, by using one of these measuring techniques you can be sure the part will fit.  Happy machining, JR49


----------



## markknx (Apr 12, 2015)

One other matter to consider when using a nut or even a plug gage  you have no real way to know how close you are. As in the nut won't start I know it is to big but how much to big? so you either take many small cuts or risk over cutting. As a hobby guy and not doing a lot of work for others. nor being a machinist just a metal worker. I use a cheat of getting close then using a die. Yes I know I should be stoned. But I do have wires and played with them a little. but my work is never that critical. But I do respect the wisdom.


----------



## randyc (Apr 12, 2015)

RVJimD said:


> I may have missed it but, is there anything wrong with using a nut if you have one the correct size and TPI to check?
> 
> Jim



Nothing wrong at all for the most part.  There may be occasions where a bit more precision is needed or where it isn't practical to use the mating part to check the thread fit.  Here's a hypothetical example, using your airplane avatar as inspiration - keep in mind that this is a very simple-minded hypothetical situation:

Vibration over time has caused a fastener from the engine in your home-built experimental aircraft to be lost.  You want to make the replacement part and have obtained suitable high-tensile stock.  The stock is chucked in your lathe and you've started to cut the threads when you realize that you have no way to check the fit of the fastener to the part.

If you remove the fastener from the lathe (to try the fit in the engine tapped hole) it will cause the threads on your part to be "out of time" with the lead screw when the part is replaced in the lathe for further thread cutting.

With a set of thread wires, or thread micrometers, and a copy of "Machinery's Handbook" this becomes a non-issue and does NOT require the part to be removed from the lathe.  You simply look up the OD and PD of the required thread size and continue threading on the lathe until your measuring tools indicate that the part is within tolerance.

If the fastener is one of several fasteners of the same type in your engine, the task is even simpler:  remove one of the other fasteners and measure the PD with thread wires or micrometers then machine the new fastener to the same dimension without removing it from the chuck.

(Note that if the new part was held between centers in the lathe using a lathe dog, it _could _be removed from the machine, checked for fit and then replaced in the lathe for further thread cutting.  But this was just an example)


----------



## randyc (Apr 12, 2015)

British Steel said:


> Talk of thread wires reminds me - I poke 'em into a wine cork at roughly the right spacing. Any excuse to open another bottle
> 
> Dave H. (the other one)



Dave, that is one of the cleverest ideas regarding thread wires that I've ever read !  I might well be able to use thread wires again, even with my shaky hands, using your idea.  Thank you VERY much !


----------



## Fldvr (Apr 13, 2015)

Thanks for all of the information, there is a lot I've not been exposed to as of yet but the discussion here is great for
me to think about.

I can see my technique needs a little more experience behind it but when I run the compound per the .0457 depth for
the 5/8-14 Bsp theads it comes up a little short. I ended up cutting until I could get a threading die on it and everything
worked out ok. Now to do 49 more.


----------



## JT. (Apr 16, 2015)

http://www.driehoekberekenen.be/

i somthime use thise one

angle A is your cutting angle (30 ore 29.5 -29 etc.
angle C = 90 dg
side B is your(crosslide) depht
thenpush  calculate and the side c is how mutch you need to move your  compound to get your (crossslide ) cutting dept


----------



## Fldvr (Apr 16, 2015)

Jt thanks for that visual representation. The math was not clear to me until
I could "see" it visually.


----------

