New to me - Colchester Triumph

[Fastdruid]

Apparently you should set it for 29.5 degrees to avoid rubbing altogether.

Just to clarify, it has to be less than half the angle. Typically 0.5°-1° less.

I found this with a nice explanation and diagrams why it has to be that as well as why feeding straight in "works" if you have a decent unworn lathe but could cause a taper or wandering thread if it is worn, not as stiff or it pushes the workpiece out of alignment. https://rick.sparber.org/spt.pdf

So 29°-29.5° for a 60° metric and UN (UNC/F) threads, 26.5°-27° for a 55° imperial (BSW/F etc) and (~22.75°-23.25° for the 47.5° BA )

 

[Pete.]

I found this with a nice explanation and diagrams why it has to be that as well as why feeding straight in "works" if you have a decent unworn lathe but could cause a taper or wandering thread if it is worn, not as stiff or it pushes the workpiece out of alignment. https://rick.sparber.org/spt.pdf

Russ of atlas_craftsman pointed out that with the cutting force on both sides of the
cutter, there is no consistent pressure on the leadscrew and halfnuts. The result is
that any backlash will show up as a wandering thread. The methods shown below
don’t have this problem.

Doc of atlas_craftsman wrote – “... I believe the helix on the lead screw
provides constant pressure towards the headstock , eliminating backlash or a
drunken thread ...the straight in bit has pressure perpendicular , but there is
pressure to the left by the driving of the lead screw...” So I guess Russ and
Doc will have to go outside and settle the matter ;-)

Russ needs to sit down and shut up.

 

[Screwdriver]

That description of equal pressure on the toolbit actually makes perfect sense to me. I can see how that would allow it to wander within the backlash of the leadscrew if you do a "plunge cut" with a threading tool.

Rather than "shut up" I'd be more interested to hear why anyone would say that proposition is false.

 

[Pete.]

Because the leadscrew has to push the weight of the saddle and apron along the bed. Unless it's riding on air bearings the lash will always be taken up as friction acts against the direction of travel.

 

[minimutly]

Because the leadscrew has to push the weight of the saddle and apron along the bed. Unless it's riding on air bearings the lash will always be taken up as friction acts against the direction of travel.

I'm with @Pete. on this. Makes sense to me.
What happens if you screwcut over a worn section on your leadscrew? Does it transfer straight onto the workpiece?

 

[Munkul]

Well put Pete. Russ's theory is bunkum.

 

[Screwdriver]

Because the leadscrew has to push the weight of the saddle and apron along the bed. Unless it's riding on air bearings the lash will always be taken up as friction acts against the direction of travel.

If you pressed stop during a threading operation, would you be able to move the toolpost back and forth by hand within the backlash of the main screw?

genuine question.

 

[Munkul]

If you pressed stop during a threading operation, would you be able to move the toolpost back and forth by hand within the backlash of the main screw?

genuine question.

No, since the tool is engaged in the workpiece...

 

[Lewis_RX8]

More testing on the lathe today

First of all thanks to @Munkul for sharing his findings on carbide inserts in this thread https://www.mig-welding.co.uk/forum/threads/carbide-turning-inserts.114318/page-2 , Particularly the speeds and feeds

So, bear in mind this is gummy black bar, maybe EN1, maybe ungraded. This was a 0.5mm DOC, 25mm dia, 1000rpm, 5 TPR feed.
It's almost flawless! Again, pictures pick up more than the naked eye does, it's almost mirror finish. If it was a better steel, I think it would be flawless.. but then again, better steels give better finishes anyway.

So blatantly copied them on my lathe as close as I could RPM wise was a bit faster but this was the result, The best finish I have got so far using a 0.4mm TNMG tool however still lines as I experienced before but more shine however to be fair the lines look worse on zoomed camera than in real life but still apparent and acts like a little file on the edge of your fingernail , Still working to fix the lines but getting there also need to try fizzy's recommended tools for aluminium but using what I have now this is the best.

Here is a video -

Now back to thread cutting thanks to Kram for the table was helpful . still messed up one pass but managed to recover it mostly get a much nicer thread IMO. Did scratch patch then set it to 0 on my high tech DRO lol , then did repeated smaller passes down to about 1.18mm depth required for M14 x 2 .

Just off the cutter a bit of chatter where I ploughed it in too much by accident but much much less and less ripping/tearing action from the cutter more actual cutting and I tried some WD as lube aswell.

Cleaned up a bit and magnified, Pretty pleased a satisfying process to watch but the reverse action keeping worm nut engaged waiting for motor to spool down and up with VFD gets a bit tiresome already haha .

I believe I am right in saying the triumphs threading dial is for imperial only so will need to keep reversing for metric only but imperial I have the dial and rapid threading unit so that's a bonus. Shame I don't use imperial much at all

Cheers for the help everyone

 

[Pete.]

No, since the tool is engaged in the workpiece...

Quite right. I'd also probably be cursing the breaking of another insert.

No matter how you look at it the carriage is being driven against friction. If the friction was insignificant no-one would be able to take a facing cut without locking the saddle lock.

 

[Dr.Al]

...but the reverse action keeping worm nut engaged waiting for motor to spool down and up with VFD gets a bit tiresome already haha .

I don't know whether yours is the same, but my VFD has a brake option. You have to add some high power load resistors to give the energy somewhere to go, but it stops very very quickly (which is nice when you're threading up to a shoulder and have to keep the leadscrew engaged).

 

[Munkul]

I had lines like that in my finishes Lewis, before I rebuilt my lathe... I think it was mostly to do with a filthy disgusting carriage rack and pinion. Worth a look?
Glad you're getting there Threads look good!
I got into the habit of changing spindle speed range when reversing, just to speed things up...! I imagine if you play with the ramp up and brake settings in the inverter you could get a bit faster?

 

[Lewis_RX8]

I don't know whether yours is the same, but my VFD has a brake option. You have to add some high power load resistors to give the energy somewhere to go, but it stops very very quickly (which is nice when you're threading up to a shoulder and have to keep the leadscrew engaged).

Ah yes it does and that would be a good use for it actually , I have been stopping with the clutch that disengages at the motor pulley but could keep it engaged and use brake function , Dont want it slamming into reverse too fast its on the threaded and taper chuck holding not cam lock so will check on that periodically.

I had lines like that in my finishes Lewis, before I rebuilt my lathe... I think it was mostly to do with a filthy disgusting carriage rack and pinion. Worth a look?
Glad you're getting there Threads look good!
I got into the habit of changing spindle speed range when reversing, just to speed things up...! I imagine if you play with the ramp up and brake settings in the inverter you could get a bit faster?

Ah good to know I'm not the only one with the lines issue seemed to be hard to find a similar problem or fix online , I have not rebuild my rack and pinion yet however have done the compound and cross slides so the pinion probably needs some attention instead of just me squirting new oil. When you say rebuilt do you mean just cleaning it all out then back together with fresh grease/oil , Thats all I have been doing with other bits not quite into scraping or anything yet for worn parts.

Yea changing speeds would certainly speed it up rather than watching it go back slowly will give that a shot.

 

[Munkul]

When you say rebuilt do you mean just cleaning it all out then back together with fresh grease/oil , Thats all I have been doing with other bits not quite into scraping or anything yet for worn parts.

yeah that's all, I had to remove the rack from the bed before the regrind so it got a good clean up before reassembly. It was so caked in grime that the teeth looked worn out. Once cleaned, the wear was minimal.
Same with the pinion. You maybe can't get to the pinion without dropping the apron (not a bad job really) but you could certainly clean the rack teeth and try spraying something at the pinion teeth from the side...

 

[fizzy]

Ah yes it does and that would be a good use for it actually , I have been stopping with the clutch that disengages at the motor pulley but could keep it engaged and use brake function , Dont want it slamming into reverse too fast its on the threaded and taper chuck holding not cam lock so will check on that periodically.


Ah good to know I'm not the only one with the lines issue seemed to be hard to find a similar problem or fix online , I have not rebuild my rack and pinion yet however have done the compound and cross slides so the pinion probably needs some attention instead of just me squirting new oil. When you say rebuilt do you mean just cleaning it all out then back together with fresh grease/oil , Thats all I have been doing with other bits not quite into scraping or anything yet for worn parts.

Yea changing speeds would certainly speed it up rather than watching it go back slowly will give that a shot.

Before you do anything get one of those tools and a few different tips for it. Not a fortune around £30!
They don't give a polished finish but very smooth with no lines hopefully.

 

[Lewis_RX8]

yeah that's all, I had to remove the rack from the bed before the regrind so it got a good clean up before reassembly. It was so caked in grime that the teeth looked worn out. Once cleaned, the wear was minimal.
Same with the pinion. You maybe can't get to the pinion without dropping the apron (not a bad job really) but you could certainly clean the rack teeth and try spraying something at the pinion teeth from the side...

I was thinking of the apron coming off for that job but it's easy enough to check the rack with the apron on like you say may take apron off for a clean anyway depending on what its like. There is not a huge amount of backlash on the wheel so don't think they are terribly worn which is good.

Before you do anything get one of those tools and a few different tips for it. Not a fortune around £30!
They don't give a polished finish but very smooth with no lines hopefully.

Waiting to hear back from jenny at JB cutting tools so looking forward to trying it, Found your youtube video on it with a very nice finish.

Should still be able to get a polished finish with the inserts designed for steel on it I would think , The aluminium ones also look good for sneaking up on dimensions for hobby users anyway as you need to take off about 0.5mm cut for a good finish on the steel cutting ones.

 

[fizzy]

I was thinking of the apron coming off for that job but it's easy enough to check the rack with the apron on like you say may take apron off for a clean anyway depending on what its like. There is not a huge amount of backlash on the wheel so don't think they are terribly worn which is good.


Waiting to hear back from jenny at JB cutting tools so looking forward to trying it, Found your youtube video on it with a very nice finish.

Should still be able to get a polished finish with the inserts designed for steel on it I would think , The aluminium ones also look good for sneaking up on dimensions for hobby users anyway as you need to take off about 0.5mm cut for a good finish on the steel cutting ones.

I did get a lovely mirror finish with a cnmg or similar the other day but I was taking a VERY heavy cut. Overshot as well - much better to sneak up on it which is where these tools come into their own. Not everyone wants or needs to take a 1/4" cut in one pass

 

[Lewis_RX8]

I did get a lovely mirror finish with a cnmg or similar the other day but I was taking a VERY heavy cut. Overshot as well - much better to sneak up on it which is where these tools come into their own. Not everyone wants or needs to take a 1/4" cut in one pass

Yup also with those cuts need to hide behind one of these from red hot bits of metal shooting at you

 

[Pete.]

Ah yes it does and that would be a good use for it actually , I have been stopping with the clutch that disengages at the motor pulley but could keep it engaged and use brake function , Dont want it slamming into reverse too fast its on the threaded and taper chuck holding not cam lock so will check on that periodically.

Those tapers are designed for rapid stopping and starting. Yuo don't have to worry about the chuck coming off.

 

[Hood]

@Lewis_RX8 just wondering if you are using the power feed when you are getting these marks or just feeding by hand?