Parting off | 5 Secrets to Success

May of us struggle with parting off on the lathe and in this video I share my top 5 tips for successful parting off.

[@joell439]

The video of yours I’ve had the pleasure to see. Extremely high value production. 👏 I’ve just now subscribed and look forward to devouring the rest of your uploaded content. Thank you for sharing 👍👍😎👍👍

[@20MaRk23]

Thanks for the tips. i will check everything agian tomorrow.

[@Rambleon444]

A little fan is always nice to blow cutting-oil smoke away from you.

[@jadymulqueeney]

Thanks great tips

[@mrayco]

Not even only carriage must be locked cross slide and compound must be very tight ...my opinion

[@AfricaTwin-Stuff]

Hi mate. Just stumbled on your channel. I see you have the same lathe as myself. Can you tell me where you bought the quick change tool post (and it’s specs/model)? I haven’t been able to find one to suit. I live in NSW on Oz. Thanks.

[@SS-Workshop]

My tool post is a Chinese clone 250-100 series, I got it from AliExpress as none of our local suppliers in NZ had them that small. The actual model is 250-111 that is the wedge type which is meant to be more ridged than the alternative piston type. One thing to note is I had to bore out the internal sleeve and turn a new centre sleeve that fitted the step in the mounting on the top slide. This was then TIG welded into place but the sleeve is threaded in as I later found so it might even be possible to unthread the centre and make one to fit that. All the 100 series tool post accessories fit them so you can get holders from any supplier.

[@AfricaTwin-Stuff]

@@SS-Workshop - thank you for your reply. That’s very helpful.

[@paulambry]

Excellent. Clear, concise and effective. Thanks.

[@paradiselost9946]

2:20 is about the most critical... TIP GEOMETRY. get that wrong, and nothing else matters. look at how the inserts shape the chip so its NARROWER than the width of the slot. general practise on hss is to set the tip over a bit so it parts cleanly. and then what happens? the chip is WIDER than the slot. so what invariably then happens? CRUNCH. you have to split the tip, vee them out, so you have TWO edges cutting on either side of the groove, forcing the chip to fold in the middle and eject from the groove properly. push the split to the left of central, and it parts off the work neatly. done properly, you should end up with a lil nib that resembles a compression olive. barrel shaped.

[@smallcnclathes]

A sub of mine using a single piece carbide insert parting tool found that by centering his tool post above the support on the topslide he was able to go from terrible parting at 500 rpm to good parting at 2000rpm, he was rather pleased.

[@SS-Workshop]

Good tip, I know my quick change tool post doesn’t help for a start and getting over the top of the top slide would reduce the movement even more.

[@terrycannon570]

Please explain this. I am having trouble using carbide cutting inserts at high speeds.

[@smallcnclathes]

@@terrycannon570 Hi Terry, parting or turning, what material, what diameter, what type of insert, so many unknowns make it difficult to help.

[@terrycannon570]

@@smallcnclathes parting on mild steel 3/4" diameter

[@smallcnclathes]

@@terrycannon570 I would expect to turn that at somewhere between 1700 and 2400 rpm using spray mist coolant

[@smallcnclathes]

I use a small cnc lathe but most of what I do is applicable to a mini lathe 1. Lube: Yes, although I do part a lot of brass without. 2. Speed: I usually part at the same speed as I turn. 3000 rpm on smaller parts, 1500rpm for large parts. So yes the diameter plays an important part in the surface speed 3. Lock carriage: Yes, or you risk cutting a dome shape and breaking the tool, they don't bend well. 4. Close to chuck: Yes, 3mm is good, a lot less than shown here. 5. Tool: As I do production work, I only use carbide insert parting tools. I have heard that some inexpensive (25aud) carbide insert parting tools from eBay work quite well. To get the tool on centre, take a light facing cut and adjust until there is no nib. Do what ever is required to ensure the tool is square, or it will bend and break. Do not blunt your tool by jamming it up against a rule placed against the work, this is just daft. The tool should stick out from the tool post as little as possible, just enough to do the job. Parting is often the last operation following a lot of work, it is not the time to ruin the part. I have a number of parting videos on my channel, should you want to see if I know what I am talking about. I have a playlist of 4 videos on parting.

[@SS-Workshop]

Thanks for sharing, great to hear how you go about this. Wow thats quite a speed, I assume your parting at a relatively small diameters.

[@smallcnclathes]

@@SS-Workshop brass and aluminium under 30mm with carbide inserts need 3000 rpm plus, but 3000 is my top speed. My lathe is small so I make 40 dia my max. Anything larger and I buy the material cut to length. I think around 40, I drop the speed to around 1500 rpm. I use spray mist a bit, but mainly machine brass dry. Steel I will normally run at half to one third of those speeds. As an example, 10mm brass needs 9500 rpm with carbide inserts. Not many old lathes have that sort of speed!. Mine are old Hercus cnc lathes made here in Australia years ago. My parting tools were not cheap, but when you make parts to sell, you have to buy tools that will get the job done.

[@SS-Workshop]

Thanks again, very interesting, certainly much faster that I dare with manual feed. I haven’t had much luck with carbide insert parting tools to date but maybe I need to take another look.

[@smallcnclathes]

@@SS-Workshop if you do, consider a single piece tool, not a blade. The better ones have a maximum dia that they can cut, but how big do you really need to part off! The reason they have this max dia is that they have diametral support for they blade which is easily seen in my videos on my parting tools. I believe this support is essential. A good insert will be shaped such that the chip it produces is less wide than the groove it is making, which helps prevent jamming in the groove. The front edge of the tool may be hollowed out to create this effect.

[@smallcnclathes]

@@SS-Workshop I recently bought a $25 parting tool off ebay, it included 10 inserts which is insane. At just 1.5 wide the inserts cut really well. I made a couple of videos on it that I released recently. I won't be so rude as to include the url here, but they are there if you want to take a look. Please delete if you feel this is a bit cheeky. Nigel

[@freestyla101]

Wow that’s some good evidence for the effectiveness of cutting oil. Any idea why it wouldn’t cut without it?

[@roulbook1921]

Most important ; Dont hesitate! If it starts to rumble and squeek-Press harder instead of backing off!

[@jayhare2647]

I broke off 2 parting tools at tafe hopefully this helps haha

[@colinmiles1052]

Nice little video - thanks.

[@michaellinahan7740]

from what I can see your test parts are aluminium, how do you go with steel or stainless?

[@SS-Workshop]

I don’t turn much stainless but do quite a bit of mild steel, it parts ok but has a habit of digging in if the tool is to low, blunt or not smoothly advanced.

[@michaellinahan7740]

@@SS-Workshop I have the sieg C6, I use a riser block instead of the compound and have just finished a rear toolpost that I use with a tapered 2mm HSS blade for AL and Brass and a 2mm carbide insert tool for stainless and mild steel. The rear mounting has certainly improved things but the overall lack of rigidity is the main issue with the machine.As someone else has said constant feed pressure also helps so a motorised cross feed is something I am working on together with an electronic lead screw. However, if I were younger or more serious I would be looking for something heavier and greater rigidity.

[@SS-Workshop]

@@michaellinahan7740 I might have to have a go at the rear mount, there is always room for improvement on what I’m doing now. I considered the solid riser but the thought of losing the compound has kept me away from it. I keep looking at bigger lathes just haven’t found a way to justify it yet! Cheers Chris.