threading

[Holescreek]

Oops, missed something in the photo. The bit mst also be perpendicular to the work and the tip on center with the work.

 

[ksouers]

How heavy of a cut are you taking? With steel I only take about 2 thou on a pass then a spring cut or two about every fourth pass. Takes me a while, but it works for me.

 

[steamer]

When you finish the pass, back the tool out before backing it up

The backlash in your leadscrew is probably to blame....they all have it....not just your lathe.

Dave

 

[moconnor]

Hello Sid:

How many passes are you taking and at what depths?

You should take no more than a .005" depth of cut (DOC) maximum for your first pass or two depending upon the total thread depth. Then reduce the DOC as you progress, finishing with .001" and taking several 'free passes' or no infeed along the way to remove the spring in your set-up. The average thread will require anywhere from 15 to 25 passes to complete depending on the material and thread depth, etc.

For example: 3/8"-16 NC 3A

DOT = .0406" (This is the single depth of thread.)

[DOC= .75/N] where: DOC= Depth Of Cut with Compound Rest at 30 Degrees, N= No. of TPI or

[DOC= .7463/N] where: DOC with Compound Rest at 29.5 Degrees from perpendicular to lathe axis.

Just using DOC 30 Degrees= .75/N = .75/16 =.0469" call it .047" total compound rest infeed. Break this down into 15 to 20 passes. You reduce the DOC based upon the thickness of the chip as you progress.

As a general rule, I will subtract .005"-.008" from the calculated DOC applied with the compound rest and remove this amount before measuring the pitch diameter with wires. (In the 3/8"-16 NC 3A example, I would remove .042" with the compound rest.) The thread is then finished by feeding in the remainder with the cross slide straight in .001" at a pass. This will then clean up both flanks of the thread. By applying the finish cuts with the cross slide, you now have a direct relationship with the cross slide micrometer collar and the thread's pitch diameter measured with the wires. If you are using a gauge or a mating part, I use the same procedure taking .001"/ pass with the cross slide until the desired fit is achieved. In both cases it is vital to take several free passes with no infeed to compensate for spring and deflection in the part/ work/ set-up. It is important to note that your infeed with the cross slide will be more than .005" that you stopped short on the compound because you are now feeding with the cross slide at 90 degrees and it depends how your dial read (diameter or radial reduction) as to what that total will be.

This is very confusing for a beginner because there is a lot going on and many variables. The best advice I can give is to understand the process thoroughly, have a plan and practice, practice, practice. There is a great deal of hand-eye coordination that needs to be developed for successful single point threading on the lathe and like any worthwhile skill, takes practice to develop.

Regards,
Mike

 

[rake60]

Are you using any kind of a cutting fluid Sid?
A little cutting oil brushed on the part between cuts makes a
hell of a lot of smoke, but it also does a lot for keeping the chip
moving. The steel will cut cleaner and tool will not load up as
much. In short chip materials like brass and cast iron you won't
have those issues.

Rick

 

[itowbig]

hello again i dunno about all that math jumbo but its my machine for sure.
i just came back from garage and did a couple test. one i stop using reverse 2 i put a dial indictor on 3 use the dial that is on the lathe now i turned it again and got some pretty good threads. (BUT) i need to do it two more times to make sure then ill be back and post pics of what i did if it indeed works out the way the first one did.
im taking a number of passes all light. i cant do the runout grove the part need to stay the same size all the way. the bearings im useing are flat and the nut that i still got to make will tighten the bearings. there is something between the gears on the lathe and the gears in the lathe bed thingy thats not right ill have to look futher. but it seems as though when i reverse it thows it out of synk like a tooth jump on the gears from what i saw. i dunno ill keep trying.

 

[Hal]

Sid

What type of steel are you trying to thread? Some of the cold roll doesn't thread well, it rips and tears , try a piece of stress proof.

Are you using the compound to feed in at 90*, if so set your compound to a a true 29* (some compound are marked different)
By doing this you are only cutting with one edge of your cutter and putting less load on your lathe.

Hal

 

[itowbig]

ok i got it figured out. this worked for me. i said the heck with reverse and used my dial thingy & the dial thingy on the lathe. fed the cross slide doohickey straight in. i have the other slide set at 29degree mark but have not had luck using it.
(but ill keep trying) any who the threads are not real perfect but darn near close.
now ive got to make the real part and a nut (oh wait im already made) :big: hope i can get this done so i can show it off ;D

 

[ksouers]

Sid,
That looks like a big improvement! Congratulations!

Keep working on using the top slide. It really is easier to do it that way.


Kevin

 

[rake60]

Looking better Sid!

Single point threading is a craft in it's self.
I do believe you've got it!.

Well done!

Rick

 

[Holescreek]

i said the heck with reverse and used my dial thingy & the dial thingy on the lathe. fed the cross slide doohickey straight in. i have the other slide set at 29degree mark but have not had luck using it.

Are you using the compound to feed in at 90*, if so set your compound to a a true 29* (some compound are marked different)
By doing this you are only cutting with one edge of your cutter and putting less load on your lathe.

Sid, From your last photo we can see that you have the compound set at 29 degrees from horizontal instead of 29 degrees from vertical. Rotate your compound to 90 degrees (perpendicular to the shaft) then 29 degrees from there. Infeeding must be done with the compound handle, not the crossfeed handle as stated above. Infeeding with the crossfeed causes the bit to cut on both sides of the angle. This is a bad thing. -Mike

 

[itowbig]

Sid, From your last photo we can see that you have the compound set at 29 degrees from horizontal instead of 29 degrees from vertical. Rotate your compound to 90 degrees (perpendicular to the shaft) then 29 degrees from there. Infeeding must be done with the compound handle, not the crossfeed handle as stated above. Infeeding with the crossfeed causes the bit to cut on both sides of the angle. This is a bad thing. -Mike

could you please show me what you mean i was under the influence that was how it was done in my pic. i would love to know how its done as threading is a real test for me.
thank you

 

[lugnut]

The way my machine is set up I have to use 61° mark instead of 29°mark, I think it's in how the compound degree is placed??? Just a thought, I know that I read this somewhere when I was first trying to thread and it worked. I also us a hand crank to turn the lathe while threading. I looked back in the information I had saved for threading and found this little discription for threading. Hope it helps:
Insure the cutting tool is sharp and a true 60*. Set the compound slide over 29° or 29.5° (on my lathe I use the 61° mark) from being perpendicular to the lathe axis. To the right for RH threads, to the left for LH threads. Now, using a thread gauge make sure the tool point is perpendicular to the lathe axis. Feed for the thread you are cutting is done with the compound slide NOT the cross slide. Start the cut some distance from the work to remove slop in the halfnut and lead screw. The cut should be done in several passes (5 or more) with two zero feed passes to remove any spring in the work. Each cutting pass should be at least .003". Use the travelling steady behind the piece to avoid deflection when required.
Stop the machine at each pass and retract the cross slide enough so the tool clears the work when you reverse the lathe WHILE THE HALFNUTS ARE STILL ENGAGED. Return the cutting tool to the same distance from the work you began the first cut with, stop the lathe and feed the cross slide back to the same point it was before retraction. In-feed the compound for the next pass and start the lathe. Repeat until thread has achieved the final depth. Double check with a thread mic or use the 3 wire method to check the thread diameter.
Use a cutting fluid on the threads while cutting - this will give the best possible finish on the threads. Nice bright & SHINY - I like Shiny!
The reason for the set-over of the compound is that it cuts a flat chip. It also allows the one cutting edge to act as a wiper giving a smoother finish than the other side. If you feed it in perpendicular to the axis the chip formed is a "V" - a great way to bugger everything up.
Was that you John?


Mel

 

[Majorstrain]

Well that's another thing I've learned, thanks Lugnut. :bow:

Now if someone could post a pic of the setup from overhead the cross slide, I can make certain that my brain cells are linking up in the right order.
(re. right offset for right hand thread etc.)

Thanks
Phil

 

[Maryak]

Two ways to skin the threading cat.

Hope this helps. ???

Best Regards
Bob

 

[Majorstrain]

Hope this helps. ???

Yep, the old brain cells are in the right line.

I assume it's 27° or 27.5° for a 55° thread, and 29° or 29.5° for a 60° thread.

I'm gonna have to make some chips to try this, that is when the temp in the shed drops below 40°C

Thanks,
Phil

 

[crankshafter]

Hi Sid.
Are you using the tailstock center : just a 2cent.

I'm leaving for some days.Grand Canary(Spain)
CS

 

[itowbig]

CS no i did not use the tailstock i know i should but this piece is 1 inch in size so i thought it was ok as long as i did not take deep cuts.

Bob yes that really clears it up for me Thank you. i can now see my setup was all wrong. Thank you all for your kind help. :bow: :bow: :bow: now ill go apply what i have learned. :bow:

 

[Holescreek]

Maryak, I have only used the compound set paralell (in your right view) for cutting acme threads. wouldn't using that method for a V thread require infeeding the compound (back to cutting on both sides) with the weakest part (tip) of the bit? We can get away with it on an acme because the tip is blunt.

1. My process is to set the compound similar to Maryak's left view but at 29.5 degrees.
2. Set the tool bit on center and perpendicular to the work.
3. Touch the tip to the work and set my cross slide dial to zero.
4. Make one pass with the tip just touching.
5. Back the cross slide out at the end of the cut.
6. Return the tool to the right end of the shaft with the X axis handwheel.
7. Return the cross slide to the zero position.
8. Feed in 3-5 thousandths with the compound.
9. Make a pass cutting at compound depth.
10. Repeat steps 5 through 9 until the pitch diameter is reached.

This has never failed me and is how I have taught others in the past. The cross slide is a zero reference only and is only used to infeed on acme threads. FWIW. -Mike

 

[itowbig]

;D i got it yeeeeee haaaaaaa
BEFORE...

AFTER...

thanks maryak (Bob) this is what i needed . now i have even better looking threads
:bow: :bow: :bow: :bow: