Rear parting

This topic has 25 replies, 14 voices, and was last updated 3 February 2020 at 15:11 by Howard Lewis.

Viewing 25 posts - 1 through 25 (of 26 total)

1 2 →

Author

Posts
1 February 2020 at 12:03 #450195
Dell
Participant
@dell
Hi all

just received rear parting tool from Cowells and upon installing parting tool even with as much packing as I can fit in, the cutting edge ( but on the bottom as it’s upside down) it is still 1.5 to 2 mm lower than the dead centre in tail stock, any suggestions?
Thanks in advance Dell
Advert

1 February 2020 at 12:03 #19614
Dell
Participant
@dell
Parting & centre
1 February 2020 at 12:32 #450201
not done it yet
Participant
@notdoneityet
You could put it the normal way up and run the lathe backwards – as long as the chuck cannot become detached, of course.

Or you could put some raising material under the tool post?

Can’t think of any easier ways.
1 February 2020 at 12:51 #450203
Baz
Participant
@baz89810
Pretty obvious answer is to contact Cowells on Monday morning and tell them the problem, they should be able to provide you with an answer.
1 February 2020 at 15:26 #450219
Dell
Participant
@dell
Thanks for reply’s

I cannot run it backwards as the chuck on a Cowells 90ME is threaded so it would unscrew, and I have sent a email to Cowells.
1 February 2020 at 15:52 #450225
not done it yet
Participant
@notdoneityet
Thought about it again, just now. Another alternative would be a parting cutter (tool) some 2mm+ less than the one you have received.🙂
1 February 2020 at 15:58 #450227
larry phelan 1
Participant
@larryphelan1
I solved that problem many moons ago when I decided to go for rear toolpost parting off.. I simply made a toolpost to suit a wide range of cutters by providing plenty of room between the upper and lower guides.

It,s not pretty but is is rock steady and it works. I just pack it up as required.
1 February 2020 at 21:03 #450283
old mart
Participant
@oldmart
I made a rear parting toolpost for the Smart & Brown model A which takes industrial 26 and 32mm blades. The top half can be turned around and it is positioned right on the edge of the cross slide. No adjustment is required, as the carbide inserts are not ever sharpened. Because the forces are upwards, I also added a rear saddle lock, which was easy as the rear screw hole for the travelling steady was in exactly the right position, and the locking screw passes through the existing tapping in the saddle. The locking clamp is easy to remove if the travelling steady is used. It is visible in the picture.
1 February 2020 at 21:13 #450286
John Baron
Participant
@johnbaron31275
I made a "Norman patent" rear parting tool post and holder for my S7LB.
1 February 2020 at 22:22 #450294
Phil P
Participant
@philp
This is my solution.

Phil

Edited By Phil P on 01/02/2020 22:24:24
2 February 2020 at 00:35 #450311
Kiwi Bloke
Participant
@kiwibloke62605
Beware of putting severe tension loads on T-slots. John Baron's toolpost obviously hasn't caused the T-slot to break (yet…), and he has fitted a reasonably long nut. I think I'd use the longest nut I could fit and would ideally spread the load by fixing the post to the nut in more than one location. The Myford/Thomas style above takes the T-slot protection further by spreading the load between two slots. The quick-change holder then adds flexibility and moves the forces outside the footprint of the post. Nothing is ideal, is it?
2 February 2020 at 05:12 #450317
Thor 🇳🇴
Participant
@thor
My rear toolpost is similar to John Baron's, except mine is clamped to the cross slide using two nuts per T-slot.

Thor
2 February 2020 at 09:04 #450332
Dell
Participant
@dell
Thanks for replies
If I shim just the front only the leading edge will it be stable enough as I have put it in without shims and held it at an angle and it lines up.
Dell
2 February 2020 at 09:44 #450342
John Baron
Participant
@johnbaron31275
Posted by Kiwi Bloke on 02/02/2020 00:35:05:

Beware of putting severe tension loads on T-slots. John Baron's toolpost obviously hasn't caused the T-slot to break (yet…), and he has fitted a reasonably long nut. I think I'd use the longest nut I could fit and would ideally spread the load by fixing the post to the nut in more than one location. The Myford/Thomas style above takes the T-slot protection further by spreading the load between two slots. The quick-change holder then adds flexibility and moves the forces outside the footprint of the post. Nothing is ideal, is it?

Actually I agree with you ! I've seen Myford's with the "T" slots broken out, and not just the rear ones. I deliberately made the "T" nut a good fit and it goes right across the bottom of the post.

I did get another piece of steel to make another support block that goes over the post and is secured in the next "T" slot, the idea being that it would effectively increase the footprint and add support. Unfortunately I have not got round to making it yet. Other projects have got in the way.
2 February 2020 at 10:48 #450355
JasonB
Moderator
@jasonb
Derek, The Cowells is intended to use 1/4" or less tools your combined blade and holder is approx 8mm that is why you can't get it high enough
2 February 2020 at 11:12 #450360
Phil P
Participant
@philp
There looks to be a lot of overhang on that setup, just be aware that the tool and its holder will flex when taking a cut.

Phil
2 February 2020 at 11:15 #450361
ega
Participant
@ega
Posted by John Baron on 02/02/2020 09:44:02:

Posted by Kiwi Bloke on 02/02/2020 00:35:05:

Beware of putting severe tension loads on T-slots. John Baron's toolpost obviously hasn't caused the T-slot to break (yet…), and he has fitted a reasonably long nut. I think I'd use the longest nut I could fit and would ideally spread the load by fixing the post to the nut in more than one location. The Myford/Thomas style above takes the T-slot protection further by spreading the load between two slots. The quick-change holder then adds flexibility and moves the forces outside the footprint of the post. Nothing is ideal, is it?

Actually I agree with you ! I've seen Myford's with the "T" slots broken out, and not just the rear ones. I deliberately made the "T" nut a good fit and it goes right across the bottom of the post.

I did get another piece of steel to make another support block that goes over the post and is secured in the next "T" slot, the idea being that it would effectively increase the footprint and add support. Unfortunately I have not got round to making it yet. Other projects have got in the way.

I recall Martin Cleeve suffered a tee slot breakage whilst parting off on his ML7; characteristically, he proceeded to replace his cross slide with one fabricated from steel.

Myfords apparently thought that their own RTP could be held by a single slot but I prefer the Duplex/GHT use of two.

Good point by old mart about the need to control saddle lift.
2 February 2020 at 11:53 #450366
Roger Woollett
Participant
@rogerwoollett53105
I agree with Jason the toolpost is "old school" and designed for quarter inch tooling.
2 February 2020 at 12:41 #450371
Dell
Participant
@dell
The overhang was just to set the height to centre and yes I can use a 1/4” HSS parting tool but some of the things I intend to make are 45mm diameter in brass so an HSS parting tool is not going to cut it ( pun intended ), if I make a wedge to set the tool on a rake would that not work ?.

Dell
2 February 2020 at 13:07 #450374
JasonB
Moderator
@jasonb
If you are careful to make sure the cutter does not get tilted sideways it is possible to just mount the HSS bit that you show in the toolpost without the holder, might just mean you can't get quite as close to the chuck jaws but only by 1mm or so.

There are also other designs of holder that would allow you to use the same type of tapered section tool but mounted higher up.

The problem with tilting the holder is you will get more negative top rake, may get away with it on brass but not dood for anything else. Also if you want to move the blase in and out it mucks up the ctr height, those 1.5mm blades can easily flex sideways so for your 45mm dia cut you would want to start with say 10mm protruding then extend another 10mm and finally a bit more to reach right in to the ctr.
2 February 2020 at 14:18 #450388
Dell
Participant
@dell
Thanks JasonB

being new to using a lathe especially one this small it is and will be a steep learning curve, I knew I would have to cut a bit then extend the bit cut then extend again , also I have been looking to see if I could find a different sort of tool so if you have a picture or link that would be great .

i haven’t started yet as I want to make everything clear in my thick head before I get going.

Many thanks Dell
2 February 2020 at 15:58 #450398
old mart
Participant
@oldmart
The main thing, Derek is to get lots of practice, read one of the books on turning and gradually the turning will become second nature. Always remember to use the safe practices and never become complacent, having a healthy respect for the machinery is the best policy.
2 February 2020 at 16:36 #450405
JasonB
Moderator
@jasonb
So first option is to do away with the holder, you will probably have to stone or grind the bottom of the tool flat as they are usually slightly angled otherwise the srews will try and tilt the tool, a small packer on top can also help.

The alternative is to use a holder like this one from Chronos that positions the 5mm high blade central to the 6mm part that is held in the toolpost rather than above it like the one you currently have. Not actually tried one of these but should think it will fit the Cowells.
2 February 2020 at 16:49 #450408
old mart
Participant
@oldmart
If using tee slots for the rear toolpost, I would definitely make use of two for stiffness. After all, stiffness and the inverted tool are the main advantages over compound mounting.
2 February 2020 at 18:47 #450427
Bazyle
Participant
@bazyle
You actually have a good way forward because the toolpost is low. Get a plate say 1/4 in thick and big enough to go under the toolpost and out across the second T-slot like the one in Phil's version. Bolt this to the underside of your toolpost with 4 csk screws. You could even consider making these small brass screws so they can failsafe.
Author

Posts