Parting tool recommendation

Thank you for all replies. They were very useful. I didn't knew about RDG tools, there are a lot of interesting stuff there. I think I'll try a T shaped HSS blade. For parting I don't like to make deep cuts required for carbide tools.

On my lathe I can't use a rear tool post. But I can reverse the motor direction. So if I mount the tool upside down it should be the same thing.

I remembered that I have this tool (20x20mm). Does it worth the effort to try to make a parting tool from it? This would mean to decrease the width of the top part to 2-3mm. A lot of grinding.

Edited By Sonic Escape on 04/08/2023 15:51:45

Running in reverse is completely safe if you do not have a screw on spindle. You do need to still get the inverted tool tip on the centre line and if the saddle can be locked it will be a bonus in stiffness. That tool you illustrated would be much too much bother to get thinned down to a usable 3mm or less width for parting. If you can use a blade for carbide inserts or a tapered section HSS tool in a holder it would be better. I would recommend getting 2 or 3mm wide tooling for most sizes of lathes for best results.

That tool could be used for grooving or be made into a general turning tool. Possibly right and left handed at the same time provided you could get it shimmed to centre line both ways round.

Edited By old mart on 04/08/2023 17:27:38

Edited By old mart on 04/08/2023 17:29:07

Edited By old mart on 04/08/2023 17:31:13

You won’t regret it, the blades are far more rigid than the plain tapered type. Several places sell them if you do a Google.

I find blades in a rear-tool post work best for me, but it's not really the cutter that makes the difference. Which tool is the wrong question, should be 'What's the best way to part-off?'

First secret is rigidity. Parting-off applies more force to the cutter, job, and lathe than most operations. They are all likely to bend, causing chatter and dig-ins. When a dig-in occurs, the forces involved make it likely be violent.

Second is the need for a steady feed at the right rate. Steady is vital, and most humans are wobbly. The tool has to cut continuously, not too deep or too shallow.

Third is making sure the cutter is aligned correctly, going straight in, not applying side-pressure because it's at a slight angle.

Fourth is making sure swarf doesn't collect in the slot and jamb the cutter. Cutting fluid in applied in quantity helps.

Example likely to fail:

• A small lathe, these are light and bendy
• protruding job, sticking out of the chuck, also bendy
• a long slim cutter in a towering tool post perched on the top-slide, perched on a cross-slide, perched on the saddle, gibs loose or unlocked. The whole arrangement is bendy, plus all the slides can twist
• Operator mounts the tool at a slight angle, causing heavy side pressure. Maybe gets the height wrong too - parting off is fussy!
• Operator moves the tool by hand. He is unsteady, and him varying the feed-rate causes the cutter to bounce. It often collides violently with the job rather than peeling metal off at a sensible rate
• Operator is low to lubricate and stop swarf jambing the cutter

Counter example likely to succeed:

• Heavy lathe - big lathes are far more rigid than small ones
• Job protrusion minimised
• Short deep cutter able to resist pressure, protruding just enough to make the cut.
• Cutter mounted on a hefty rear tool-post bolted directly to the saddle.
• Ideally run lathe in reverse. This pushes the rear toolpost and saddle down, rather than lifting them.
• Operator selects correct RPM and feed-rate and engages automatic feed. Automatic feed maintains a constant cutting force, and eliminates human error.
• Operator pays close attention to clearing swarf

Only real men can part-off on a mini-lathe. They're light and don't have a rear tool-post or automatic feed. The tools are small and bendy.

Myford size machines are much less challenging, They have more weight and probably have a rear tool-post and automatic drive. Parting off from the front is do-able, but more likely to go wrong. A rear tool-post is generally reliable.

Parting off on bigger than Myford is almost trivial. Lots more weight, and even the front tool-post is impressively rigid. Automatic drive etc available. With a rear tool-post, parting off is trivial.

My lathe is a WM280, rather heavier than a Super 7, but not massive.

I can part-off by hand using the front tool-post if I'm really careful, but failure is always an option Front-tool post with automatic feed is almost 100% reliable - mostly works, occasional grief. Rear tool-post is 100% reliable unless I do something stupid.

Dave

The center section was cut with a hacksaw?

..yes, I ran out of 'reach' - there is nearly as much blade sticking out as there is left in the tool holder..

I can't remember what the cut depth was but well over 30mm using a 19mm 'high' blade. The stock is 100mm diameter.

Just wanted to show that these tools are capable of giving good service under less than ideal conditions.

3.5 inch PB parted all the way

Hi Sonic.

Something like the 1st picture would be your best bet IMO. I've two different ones which both seem ok for the job.

You don't say for which lathe.

The one Arc Euro Trade sells i find works best in the mini lathe as the blade is a little thinner than others i've seen~ which is kinder on the mini lathes limited power & rigidity.

Regarding parting off on mini lathe, a few tips.

1 ~ never have blade sticking out more than is necessary for the job in hand.~I broke my first blade recently on 10mm silver steel,because i was too lazy to wind it back in after a bigger job .

That made me jump! Blade shattered, good job i had my safety specs on.

2~ make sure the blade is dead square to the work.

3~ plenty of lube if parting off steel.

4~ slow steady cross slide feed & i find around 250-300 rpm works best for me.

5~ lock off everything you can (except the cross slide obviously)

Edited By samuel heywood on 05/08/2023 20:24:41

Agree with Samuel Haywood, speed for mild steel 200 - 300rpm or roughly half normal turning speed. I have parted off MS dry just to experiment but normally use cutting oil. If tool protrudes say 15mm, you should be able to get a total depth of cut of 12mm or so, or around 1in. dia. I recently offered the side of the cutter up against the stationary chuck and interposed a small section HSS tool between the chuck face and the side of the parting tool as the latter was recessed due to its wedge clamp just for alignment before clamping the toolpost.  Worked OK. Parting toolholder that I'm referring to is the only one that I now use, being in my opinion, the best available - that sold by RDG Tools. Just a very satisfied user. I now always only use 3/32" wide HSS blade which doesn't bend like thinner ones. What's the point in using ultra thin blades? Save metal wastage? Tool bends and creates a concave surface on one side and a convex on on the other, both requiring facing and therefore wasting metal.

If parting very large diameters, try 3 goes at it, side by side, so you have a step each side of the centre cut thus helping swarf clearance. This is shown in L H Sparey's book, "The Amateurs Lathe" page 131. I've not tried it as anything 25mm or more goes into my bandsaw then a facing op.

John

Edited By DMB on 05/08/2023 21:54:26

Do the T-shape parting blades fit OK in the holders designed for the tapered type, or is a bit of judicious modification required?

Rob

The T type blade I have has the same dims tops and bottom edge as the standard tapered eclipse type and fit in my holder fine if that’s any help.

Does anyone regularly use a T / chipbreaker type in stainless?

.

There are probably some good clues in Sonic’s concurrent thread: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=187551&p=1

MichaelG.

My lathe is a medium size industrial machine. 750mm between centers, 140mm chuck, 800kg

3 months ago I used a brazed parting tool on stainless steel. It worked fine. Even considering that the workpiece was not supported with a live center. But it is about 5mm wide so it is wasting material. Also later I was not able to duplicate the operation. On the same type of material.

Edited By Sonic Escape on 06/08/2023 20:06:23

Thanks Bernard, I'll pick one up at the show in October and give it a try.

Rob

Just received my new blade from ARC Euro * with a GTN2 insert ; was planning to (when ever I get round to it ) make a rear toolpost for it so hopefully avoiding all the parting-off horrors I've experienced over the years. Believe me I've tried every bit of advice from you good folk on the forum over the years and still could never get a decent job / often getting jams etc with HSS blades.

Just tried the new toy on the ordinary 4 way, made sure everything was locked tight as practical, lowest gear so about 80 - 100 rpm and working on a 2in dia MS bar.

Joy! With consistent manual feed (fairly heavy) went in like the proverbial knife through butter. Brilliant!

Don't now feel a rear toolpost will be necessary for the standard type of materials I use anyway.

Regards Mike

* Other suppliers stock similar models