Single point thread cutting

[azzrock]

Sorry every one about a repeat topic.
At work I mainly do maintenance work.
We have a pretty smik little lathe. I have been trying to cut some threads but it's been a while.
Off setting the compound to 29.5 deghas not been working for me . Ends up looking like a buttresse thread.I use HSS. Does any one use the plunge or advance the compound method for thread cutting?
The threads are to support vechal development . For suspension dynos
I'm trying to make a 27mm 2 pitch to 1" unf thread adaptor. In mild steel.

[LexD]

Try setting at 60 or 60.5 degrees on the scale, that will give you half of the tool angle (30 degrees approx) from the straight in position.

[azzrock]

Try setting at 60 or 60.5 degrees on the scale, that will give you half of the tool angle (30 degrees approx) from the straight in position.

Hi mate thanks for reply. From memory the compound has a range from 0 to 40 deg. I'll have a look tomorrow . It's a better quality hafco machine made in thaiwan

[azzrock]

If I set the coupound at 0 deg. How much to I have to wind it regardinging to depth of cut and for how long. I seem to remember 2 in 1 across.

[Michael G]

... Does any one use the plunge or advance the compound method for thread cutting?
...
I'm trying to make a 27mm 2 pitch to 1" unf thread adaptor. In mild steel.

Yep. I plunge cut all the time (as in, I don't use any other method). Most recently I was doing a 2-1/8x20tpi thread nut and bolt but have recently done some worms as well.

Michael

[BaronJ]

Hi Guys,

I agree with just plunging in and using the top slide dial for the depth of cut ! A caveat though I gave up on trying to grind accurate HSS tools to get the thread form correct, so on advice resorted to pre shaped carbide insert tooling, which I now use for both metric and imperial threads.

Forget about setting compound angles, just make sure that the tool is dead square to the work and plunge in. Yes I do understand why setting the compound at an angle is recommended, particularly for buttress, acme and other large threads.

[Michael G]

... just make sure that the tool is dead square to the work and plunge in. Yes I do understand why setting the compound at an angle is recommended, particularly for buttress, acme and other large threads.

I don't even bother offsetting for larger threads - I've done buttress and ACME using plunge cutting. I leave the compound slide for syncronising the thread with the feed if I have to (as per the video where I battle the worms of doom), and feed with the cross slide.

Michael

[Dave J]

I agree, Just 90 degree plunge cut as said.

Sent from my 5007U using Tapatalk

[Jekyll and Hyde]

Like most others here it seems, I've never bothered rotating the compound and just plunge with the cross slide alone.

However, if you did want to do the rotated compound method, Techo1 will probably be correct.

The reason for this confusion that arises at times is some lathes mark zero degrees on the compound with the compound perpendicular (at right angles) to spindle axis, others mark zero degrees with the compound parallel to the spindle axis. The Asian machines seem to often do the second, and if your machine is an AL960b the pictures on H&F website show that it definitely does the second.

If zero is with compound perpendicular, 30 degrees (ish) is correct, if zero is with compound parallel, 60 degrees (ish) is needed.

The easiest way to sanity check yourself which way round you need to be is that the direction of compound movement must be aligned with the trailing flank of the desired thread.

[Don@2480]

Azzrock,
Keep trying the offset method of screw cutting as it is the best way to cut vee threads in MHO.
You are correct to offset the compound rest by 29.5˚ for 60˚ included angle threads. Half a degree less than half the included angle is the "standard".

The tool (if HSS) must be ground to the included angle of the thread, have a small nose radius achieved by honing. Then grind a rake angle of approx. 15˚ so that the leading edge of the tool is the only edge of the tool in contact with the work. Most importantly, set the tool at 90˚ to the work axis.

Zero both the dials on the compound slide & the cross slide. The depth of the cut is achieved by advancing the compound rest ONLY. The cross feed is used to withdraw the tool from the cut & must be returned to zero prior to the next cut.

Depth of cut for metric threads is found by; Depth = 0.6134 x thread pitch x 1.1434. This is the amount that the compound rest is advanced to achieve the whole depth of the thread. Variation to this calculated size may be required to suit the mating thread.

If imperial Depth 55˚threads = 0.6403 x 1/tpi x 1.1174

OFFSET.jpg Direction of tool movement.

Hope that this helps,
Regards,
Don.

[nadroj]

After adjusting the compound slide angle, are you setting up the tool bit accurately, with a screwcutting gauge?

https://www.micro-machine-shop.com/h...l_pulley_6.jpg

[Don@2480]

Nadroj,
Yes, a screwcutting gauge must always be used to set the tool at 90˚ to the work axis.
However, as the tool has a rake ground onto it, only the leading edge of the tool is set to the gauge when using the offset method.
Regards,
Don.

[azzrock]

[QUOTE=Don@2480;1993608]Azzrock,
Keep trying the offset method of screw cutting as it is the best way to cut vee threads in MHO.
You are correct to offset the compound rest by 29.5˚ for 60˚ included angle threads. Half a degree less than half the included angle is the "standard".

The tool (if HSS) must be ground to the included angle of the thread, have a small nose radius achieved by honing. Then grind a rake angle of approx. 15˚ so that the leading edge of the tool is the only edge of the tool in contact with the work. Most importantly, set the tool at 90˚ to the work axis.

Zero both the dials on the compound slide & the cross slide. The depth of the cut is achieved by advancing the compound rest ONLY. The cross feed is used to withdraw the tool from the cut & must be returned to zero prior to the next cut.

Thanks Don good discriptin.

[azzrock]

Thanks everyone. I had a success today after a few set backs.
I was using a thread form gauge to set up.
I stuffed up a few pieces when I tried to cut the second unf thread. I tried using the thread indexing dial instead of leaving the half nuts engaged.
I useded the plunge with compound at 0 deg. Ended up with a good thread.
Thanks Aaron

[azzrock]

Like most others here it seems, I've never bothered rotating the compound and just plunge with the cross slide alone.

However, if you did want to do the rotated compound method, Techo1 will probably be correct.

The reason for this confusion that arises at times is some lathes mark zero degrees on the compound with the compound perpendicular (at right angles) to spindle axis, others mark zero degrees with the compound parallel to the spindle axis. The Asian machines seem to often do the second, and if your machine is an AL960b the pictures on H&F website show that it definitely does the second.

If zero is with compound perpendicular, 30 degrees (ish) is correct, if zero is with compound parallel, 60 degrees (ish) is needed.

The easiest way to sanity check yourself which way round you need to be is that the direction of compound movement must be aligned with the trailing flank of the desired thread.

Thanks. Lathe is similar to this.

https://www.machineryhouse.com.au/L191D