Chipmaster Thread Cutting

[Piers037]

I have had my Chipmaster for a couple of years but only ever tried once before (unsuccessfully) to cut a thread.

Tonight I had a go at cutting a practice thread for a ER32 collet holder that I am making. The tread, if you can call it that was #### house....
image.jpgimage.jpg
The process I am using is:

hand ground HSS cutter checked with fish tail
compound slide set at 60 deg to the bed.
Set tool on centre height
touch off work and set cross side dial to zero
engage half nut in the same position for each cut
engage half nut clear of work to take up back lash
At the end of each cut, screw out cross slide and disengage half nut.
hand crank carnage back
re zero cross slide and wind in 5 thou cut on compound.

the thread appears to be galling up and ripping off the treads

What am I missing...

cheers

Piers

[Stustoys]

This might sound a little harsh but, are you sure this was the right job to practice on?
That aside, does your lathe have a metric leadscrew?(It does look like you are getting repeat pick up but its hard to be sure). Do you have the right gear on the thread chaser?
Did you try and couple of passes with no infeed?

Stuart

[morrisman]

Piers

You set the top slide over about 29 to 30 degrees .... not 60 degrees .

And your tool looks nice but it does not have any side rake ....

Did you use any lubricant ? eg neatsfoot oil works OK .

Mike

PS with some side rake on the tool , and feeding in with the top slide ( not the cross slide ) you should see the swarth peeling off in small curls , rather than what you have got in your photo .

[Ueee]

Hi Piers,
As mike said you need some side rake, running from left to right, i grind mine parallel with the right hand side angle. 5thou is fine for the first few cuts, but you need to shallow it out for finish cuts, and take a couple of spring cuts. I never swing my compound any more, but thats a whole other kettle of fish. Best to get it right with the compound set to 29deg first. I really like tap magic as a lube for threading.

Cheers,
Ew

Edit, watch from about 10.00 of this, you can sort of make out the tool rake and chips you should get. Making a BXA quick change toolpost nut - YouTube
What speed were you running at?

[j.ashburn]

Piers

You set the top slide over about 29 to 30 degrees .... not 60 degrees .

And your tool looks nice but it does not have any side rake ....

Did you use any lubricant ? eg neatsfoot oil works OK .

Mike

PS with some side rake on the tool , and feeding in with the top slide ( not the cross slide ) you should see the swarth peeling off in small curls , rather than what you have got in your photo .

with you all the way Mike. I always try a cut on a bit of scrap when setting. Want a hint for recycled bar car axles from the wreckers or your favorite recycler[metal] another source is mc pherson strut inner shafts is hard though and is still relatively easy to machine.

[j.ashburn]

with you all the way Mike. I always try a cut on a bit of scrap when setting. Want a hint for recycled bar car axles from the wreckers or your favorite recycler[metal] another source is mc pherson strut inner shafts is hard though and is still relatively easy to machine.

with a thread that small in length I have a mandrel handle[ crank that goes in the h/s spindle. Leave 1/2 nuts engaged .[wire them up so cant jump out when the load is released[old machine you need to do this]Pull out the power plug[SAFETY FIRST}and wind the handle in a few thou on cut. wind back cut on wind on close to your final depth of thread spring cut 2-3 times trying the nut as you go. plenty of lube John.

[sossity]

First post on here and although I'm probably not really qualified to give advice as I have only just learned how to do a reasonable thread, maybe describing all the mistakes I made might help someone else out. It took me four attempts to get the first one right and I found a different fault each time. .
My mistakes left my thread looking a bit worse than yours but if I had stopped when I noticed it going wrong, it would have looked very similar.

I tried a light cut, then went back and made another light cut to make sure everything kept in alignment, which it did. I thought this tested my method as being correct, but no!
First I noticed the DRO on the cross slide was indicating it was moving a lot when I started to do a deeper cut. I figured this was knocking the sync of the thread out, so I had to modify my lathe to be able to lock the cross slide. First problem fixed.
Tried the light cuts first again on a new bar, and it looked good again.
Started making the thread and it looked ok but then went wrong after a couple of deeper cuts. Figured out a really dumb mistake I was making. I was reversing the lathe using the gearbox instead of just reversing the motor. Sometimes the gears would mesh in the same teeth by chance, and make it look like everything was going ok. Then the wrong teeth would take up and I was well out of sync and cut up the thread. Pretty embarassing to admit cos it seems so stupid now.
Next mistake was I got a thread of sorts but I had used the 30degree mark on the compound rest which gave me 30degrees to the bed not 30 degrees to the workpiece. So it looked like a sawtooth.
The threads I mostly want are metric and everyone says not to disconnect the halfnuts if your leadscrew is imperial. I read a great method someone else described on the web somewhere. Basically, you do disconnect the half nuts when you reach the end and back out the cutting tool. You stop the lathe motor and let it slow. You can take quite a few seconds to let it stop, no need for a foot brake. The trick is to then reverse the motor and catch exactly the same number on your thread gauge on the way back, then engage the half nuts at the same point. Then let it travel back to the beginning and stop the motor again, but leave the half nuts engaged, ready for the next run. That way evertyhing is synced to the same point on the leadscrew. Its pretty hard to miss getting the right point using the thread number thing, but if you do, you can just reverse again, and pick it up the next time.

[Steamwhisperer]

Hi piers,
I sent you a PM.

Phil

[Piers037]

Thanks everyone for your replies and tips.


Stuart

"does your lathe have a metric leadscrew?"

No. Can select metric threads with the gearbox

"Do you have the right gear on the thread chaser?" Not sure what you mean

"Did you try and couple of passes with no infeed?" No. Good idea. Will give it a go when next in the shed

Cheers

Piers

[Ueee]

Hi Piers,
If your cutting a metric thread (which i presume you are since the ER collet should be 1.5mm pitch) you cannot disengage the halfnuts whilst cutting, you have to reverse the lathe. The gears Stu is talking about are for metric machines, you need different sized gears for the thread indicator depending on what pitch you are cutting. With imp you only need the one.

Cheers,
Ew

[Piers037]

Mike,

"You set the top slide over about 29 to 30 degrees .... not 60 degrees"

see photos. The 60 degrees is the angle showing on the lathe compound.image.jpgimage.jpg


"And your tool looks nice but it does not have any side rake .... "
I think I have side rake but it was not clear in the other photo. Better photos attached.
image.jpgimage.jpg


"Did you use any lubricant ? eg neatsfoot oil works OK ." Only whatever is in the oil can

Thanks Piers

[Piers037]

Hi Ewan,

Yes I am cutting a 1.5mm metric tread.

What is the issue with disengaging the half nuts with an imperial lead screw? I have not heard about this!

Cheers

Piers

[Stustoys]

What is the issue with disengaging the half nuts with an imperial lead screw? I have not heard about this!

You cant be sure that the spindle and leadscrew are at the same point in their rotation so you will cut the thread in a different spot each time.

Those photos show side clearance. Top and side rake or on the top......... I've been known to cut threads without either.. but dont tell anyone.

Stuart

Helps you hit submit when you type a post lol

[azzrock]

I have had my Chipmaster for a couple of years but only ever tried once before (unsuccessfully) to cut a thread.

Tonight I had a go at cutting a practice thread for a ER32 collet holder that I am making. The tread, if you can call it that was #### house....
image.jpgimage.jpg
The process I am using is:

hand ground HSS cutter checked with fish tail
compound slide set at 60 deg to the bed.
Set tool on centre height
touch off work and set cross side dial to zero
engage half nut in the same position for each cut
engage half nut clear of work to take up back lash
At the end of each cut, screw out cross slide and disengage half nut.
hand crank carnage back
re zero cross slide and wind in 5 thou cut on compound.

the thread appears to be galling up and ripping off the treads

What am I missing...

cheers

Piers

hi mate. have you tried the other screw cutting method.ie advancing the compound slide. Compound slide square. tool set up to job with a screw cutting gauge.
now my memory. Advance the compound slide (i cant remember the ratio half the depth of cut) a little. after your first cut so the tool isn't cutting on both sides.
is there enough clearance on the tool. center height is very important for a good finish.
How about leaving the half nuts engaged for the hole job. just stop the machine at the end of the cut
wind out the tool reverse the machine past the start of the job set the doc and cut again with out
disengaging the half nuts..go slow
aaron

[Piers037]

Thanks everyone for your responses. I am pretty shaw this is the issue.

I will have a go and not disengage the half nuts and see how it threads.

Cant wait to try it out but am unlikely to get any shed time until the weekend.

Cheers

Piers