Mini Lathe Rear Cut Off Tool Post Upgrade

G'day,
In this video I will be making a rear cut off tool post for my sieg c3 mini lathe. Parting is one of the weak areas of these mini lathes, due in part to a lack of rigidity and power. I have seen people mount parting tools upside down and run the lathe in reverse to prevent the tool from getting pulled into the workpiece to achieve better results.
My lathe does not have a reverse, so a rear cut off tool post would be needed to achieve the same result. With my new cross slide with t-slots (made here: • Lathe Cross Slide Rebu... ) I am able to now machine a riser block to mount by parting tool holder that is made for my Sherline lathe.
Lathe; Sieg C3 7x14 mini lathe
Mill: Sieg X2.7L
#machining #lathe #minilathe

[@joels7605]

Excellent information. Thanks for providing this, especially that you proved the cutting performance was similar to normal parting. Well done, sir. Thank you.

[@chazmakarowski5429]

High rake tools are a great option for low power tools as this mini lathe since it gives more of a shearing action over a tearing action for the cut which requires less power and can leave better finishes. The downside of course is that the tool geometry is weaker and loses the ability to dissipate heat. If the aluminum wasn't cutting well with the positive rake tool my guess would be that it did not have have enough cutting oil to prevent build up on the edge. Being on the underside like that would make it harder to apply the oil directly before the cut compared to the tool being the other orientation.

[@shedmanx3640]

I understand exactly what you mean by unforeseen events in your part of the world. I live in Victoria, Australia and buy all my metal as offcuts on EBay or sellers that deliver on FB market place. I didn’t know about the running the lathe in reverse trick. My lathe has reverse so I might give that a go. Thanks.

[@dogphlap6749]

Thank you for the video. Very interesting. Perhaps it is time to investigate (electrical) means of reversing your lathe motor. A switch to reverse the wiring to the stator coils will do that fairly easily if they are accessible, if not a motor capable of being reversed in that manner might be worth the investment in time and dollars (I find screw cutting right hand threads is often less traumatic with my lathe in reverse and the tool mounted upside down).

[@homemadetools]

Nice job as always. We shared this video in our homemade tools forum this week :)

[@shawnmrfixitlee6478]

I have often thought about trying this . Great info !! ENJOYED..

[@MurrayC]

Looks like a good mod, stay safe

[@artisanmakes]

Thankyou

[@marilynjernigan4673]

well it's a lathe kzbin.infoUgkxN9zrzkkhnjUF5PQbuA_B1gYdsfCu9k6z but it wasn't what i would have anticipated. Headstock, tailstock, carriage apron are manufactured from aluminum now not cast iron. The spindle diameter for the bearings is too small allowing for a few play in the spindle so I am using some blue Loctite to take out the play.

[@BLECHHAUS]

Nice work! Made a similar rear toolpost out of steel for my Minilathe and it cuts steel, stainless steel and titanium like hell :-)

[@artisanmakes]

Titanium on a mini lathe is very impressive. Never attempted it on mine.

[@BLECHHAUS]

@@artisanmakes Titanium is roughly the strength of steel. Choose either indexable inserts for aluminum or very sharp HSS tools with a cutting angle between steel and aluminum. Cool well, especially when parting off. In contrast to the other metals, the chips do not dissipate the heat. This means that the workpiece will warm up quickly. Drilling: normal HSS drills, but lubricate well otherwise the drills will rub into the hole. Then you can do it. Titanium is just a metal too ;-) I will soon post a video making a ring out of titanium. External turning, drilling, internal turning, parting, everything included.

[@YooProjects]

Great project man. Keep going forward 💪

[@cavemaneca]

This can be useful to have in certain setups where you can use it without having to do as many tool changes. However, like you said with your improved cross slide setup it's already rigid enough so it may not be a real improvement in that way. Maybe with a motor change for something higher torque/lower rpm you could part off steel better.

[@artisanmakes]

Cheers, I'm looking into a new gearbox to power the lathe so I can better reduce the rpm.

[@sumgai7]

At around 4:16, when you're talking about the positive rake blade - one can also just quite obviously see the blade FLEXING (leftward); when you switch to the zero rake blade, well, it's quite a bit THICKER, and doesn't flex! It just seems to me that has rather a lot more to do with it than rake, no?

[@artisanmakes]

possibly, but the rake was the factor most responsible for the aluminium catching on the edge of the tool

[@canberradogfarts]

@@artisanmakes NO. The complete lack of side relief, on a thin blade, with the wrong rake, on a cross slide with functionally no vibration absorbing mass is why!

[@artisanmakes]

@@canberradogfarts it probably not quite visible on camera but the parting blade has side relief ground into it from the factory.

[@brianmoore1164]

The keys for me are narrow parting blade and lower rpm. If I keep the speed below 300 rpm I can part steel just fine.

[@artisanmakes]

Cheers, I'm looking to machine a new set of change gears to drop the rpm to achieve these lower speeds

[@brianmoore1164]

@@artisanmakes That will work. Parting is one of those operations where everything needs to be perfect. Very sharp tool, narrow tool, perfectly square, low rpm, your best high pressure cutting oil and then it will behave. Love your channel. Those of us who operate the smaller lathes and mills don't have much content. Thank you.

[@quelixfenzer5108]

I have a mini lathe and for me self ground parting tools with about 2mm width, slight side reliefs and quite a bit of positive rake on not too low rpm work best. I also recomment to give your hss lathe tools a little touchup on a wetstone after grinding for a finer edge. So far I was able to part everything from Aluminium to stainless steel with some trial and error.

[@HM-Projects]

@@artisanmakes get mgmn inserts which actually work better at higher speeds. kzbin.info/www/bejne/nmfKh3yqeNRkY6s Edit: I might've been too sleepy, missed the bit about rigidity and the fact that you've already got those parting inserts.

[@chazmakarowski5429]

@@brianmoore1164 take this with the knowledge that I'm talking about larger machines, but in my experience if you run the lathe at the same speed you would for your turning tools, and you keep high pressure on your parting tool you can achieve spectacular results. Usually if my part vibrates while parting I dig my tool in harder and that will quiet it right up

[@SimJackson]

Regarding the rake on the blade for aluminium, I was always taught that aluminium cuts best with quite an aggressive rake angle on the tool, around 30 degrees, where most other materials are between 5 and 10. This could be why you were finding the tool with no rake cut better than the positive rake

[@artisanmakes]

You are right, and I might have made a small mistake here. You see I used to try and part aluminium with a 30 degree rake tool and it used to dig in and stall the motor, hence why I made this rear cut off tool. I had since reground the tool to have a less aggressive rake to prevent it biting in. However i didn't regrind it back to its original 30 degree rake angle. I'll have to try and see how it performs.

[@wizrom3046]

High rake is good for aluminium, but you have to make sure the setup is rigid and has no leadscrew backlash. That backlash slop will allow the tool to "pull in" to the job. I had problems like that with my little China 7x20 lathe, mainly fixed it by using a crossfeed clamp semi-tight, to basically tighten the crossfeed gib right up so it can't pull in to the job. Having a hand screw to tighten the bib as needed means you can run it real tight for those few scary seconds when you are parting lol.

[@andersgrassman6583]

@@wizrom3046Yeah, I tighten the gib ”excessively” for parting, and after I slacken it back to normal.

[@Pushyhog]

nice to have, and out of the way back there. A keeper. If you sold implements l would buy:) T-Cross slide is great.

[@catherineharris4746]

Nice!👍👍👍

[@jackdawg4579]

hmm. good idea, i might have to make myself one!

[@PatriotCoinRings]

Looks like you were cutting pretty easy with the Central Machinery Mini lathe there. Was that Aluminum you were cutting?

[@vesslewiththepesstle]

perhaps 180 the base and redrill the post in the correct position.

[@donmittlestaedt1117]

Thanks

[@mackk123]

It seems that another solution for the mini lathe is to reduce the speed and increase the torque.

[@НиколайКрымский-б1л]

для снижения оборотов используй контрпривод, и к тому же не обязательно пользоваться только зубчатым ремнем. внимательно присмотрись - заметно как отгибает заготовку вместе с патроном и передней бабкой, это место необходимо усилить

[@justice0952]

You should make some kind of cover for your t-slots. Cleaning them out may get annoying after a while. It’s pretty simple if you have a 3d printer.

[@artisanmakes]

Thanks for the suggestion but I haven't run I to any issues so far, shop Vac cleans them out with no issues. And i only have a DLP 3d printer and the resin does not typically stand up to wear and tear.

[@GavinM161]

Would you post a link to your tipped fly-cutter please?

[@davidrule1335]

2:22 Are you click spring?

[@Smallathe]

Nice work...

[@artisanmakes]

Thankyou

[@maciejzielinski4033]

Try ethanol as aluminum turning coolant

[@wizrom3046]

That tiny little bolt holding the toolpost down is not doing you any favours... 🙂

[@artisanmakes]

It's not really made for this lathe, its intended to work on a sherline

[@bryanknecht513]

use difrent blades, sharper one for aluminium.

[@TommiHonkonen]

I've wanted to buy a lathe and mill for so long but due to space I can't fit them. Also me being an actual real machinist I am not impressed how these work. Maybe some day tho. They might be handy to have along a 3d printer.

[@Jason710.]

I know what u mean, I was a machinist and while it is a lot weaker than a normal machine, there are more powerful ones than this one, I got a micro mark7*16 cuz there are no headstock gears and it has more power, u can run it really slow, and has better tolerances. I also am limited on space big time so could only get small machines , and if u take smaller cuts and take ur time they can still be very useful. I have an ender 3 pro 3d printer massively upgraded from years ago , but now Im more back into machining and it sits around now that I'm cutting metal again..lol

[@canberradogfarts]

Touche`

[@canberradogfarts]

Tune your lathe FIRST. Check headstock runout accrois tbe entire speed range. Get TWO temperature probes and monitor the temperature of both front and rear headstock bearings. Check without load for an hour, taking the temp every five minutes. Stop and let it cool down overnight. Repeat under medium load (YMMV) and again take temp ever five minutes for at least 30 minutes. YES you need to be making chips the whole time. After you have done ALL of this, then experiment with blades. Crawl first, then stand.

[@artisanmakes]

I replaced the bearings not too long ago, the run out is just under 8 microns with the preload I put on the bearings. Its more than I could ask from a lathe at this price point, and I don't think I could ask anything more from it.

[@dzarren]

I have found that, if anything, a set up like this is less rigid than in a conventional way. The tool post is now being lifted, and the carriage being slightly lifted off the ways. There's a strong reason for the lathe to be in reverse, and flipping the tool doesn't make sense on a small lathe, its not rigid enough. I'm surprised there was a supposed increase in performance.

[@artisanmakes]

I guess there are some pros and cons with which ever way it is set up. I think with my new compound slide the set up is that much more rigid that running it like this is okay. From my observation, I would rather it be a little less rigid than risk the parting tool digging in. Each to their own, Cheers.

[@Pushyhog]

do u now wish you had reverse??????

[@artisanmakes]

It's still not a huge issue, I work around it. If it becomes more of a hassle I can easily swap the motor out. Cheers

[@nickdibart]

I'm having a a lovely time at work trying to part a 13.5" OD, 11" ID piece of 410 stainless. It's being more troublesome than parting normally is for me. I gotta worry about work hardening also. It's a real pain in the ass sometimes!

[@crishawkins7359]

You are definitely turning the spindle too fast as you said. But you have very poor tool geometry there is WAY TOO MUCH clearance on the lower part of the tool (the top when inverted). You should have that area of the tool almost vertical. Since the part is round, as it rotates, it moves away from the tool and creates its own clearance automatically. With all the clearance you have, there is a high likelihood that the tool can be pulled into the work-piece (which is why the aluminum was grabbing). The top rake on your tool wasn't the problem with the aluminum, it was the front clearance....

[@chrisford9045]

Yes, you are right. The front clearance regulates the feed rate and prevents the tool from being pulled into the workpiece when ground at the correct angle

[@JesseSchoch]

There are many good comments here but the main reasons parting is difficult is due to the harmonics caused by spindle flex due to the distance from the cut to the spindle bearing and the cumulative leverage of the tool holder. For the first issue there isn't much you can do beyond getting a chuck that is not as long. "Winky's Workshop" did a series of videos on this topic, though he didn't really cover deeply the harmonics and natural frequencies which are what produce the chatter. Reducing the distance changes the harmonics which improves things like parting. The 2nd issue is based on the geometry of your ways and the position of the cross slide and compounds in relation to the ways. When you move the cutter to the back and flip it upside down the cross slide is pulling up on the bottom surface in the back way. This surface is not machined well on mini lathes and has a limited surface area. It also is not rigid because of the grub screw adjustments in the back of the cross slide. The reason reversing the motor with the rear cutter position works well is that it pushes down on the rear way which provides a very large contact area with little flexibility. Your way pulls it up and unless you rework your rear cross slide way adjuster I doubt you can get good results over having the tool in the normal position on the front way. As the cross slide "pulls up" it either digs in or backs off which produces the chattering with a regular frequency that is driven by the tool geometry and spindle speed combined with the natural frequency of the spindle flexing.

[@artisanmakes]

At this point i'll take what I can get. These lathes just aren't up for the job. The lathe I used to machine on probably weighted 10to15 times this. Considering how little i part anyway, im going to leave it at this. Cheers

[@JesseSchoch]

@@artisanmakes I just made a whole video on the topic that I think could help you out. maybe you can watch it, baseline your machine, and finally share the measurements?

[@ChrisHarmon1]

So you're one of the five people in AU. That town makes a lot of noise for being so empty...

[@canberradogfarts]

Your mill is "out of tram."

[@artisanmakes]

i know its out of tram, the adjustment gibs stripped in the hole so I'll have to drill it out to fix it. Parts still fall within tolerance so its not super high in the agenda.

[@jackkuehneman9300]

Pretty soon youre gona be machining some firearms if your country decides to keep recreating Stalin's Soviet Union..

[@DolezalPetr]

cutting speed is completely wrong

[@artisanmakes]

I talked several times in the video, I have a gear driven lathe and the lowest speed is still too high. I need to machine some new pulleys to change the ratio. Not optimal but I have to work with what I have available to me, Cheers.

[@DolezalPetr]

@@artisanmakes you need to calculate the cutting speed and choose a proper tool for it, for a D=25mm round steel stock and a cutting speed of 100m/min you would need 1200 rotations per minute, for 20m/min you would need 250 rotations per minute

[@canberradogfarts]

You need to heavily study blade geometry. One blade does NOT cut all well. Adjusting just the speed is a recipe for a Fuqit Bucket full of scrapped parts. Your steel blade needs SIDE RELIEF. Heck, all of them could befit from side relief. Side rubbing is where a butt tonne of your power is getting lost in your parting ops.

[@canberradogfarts]

P.S. Get rid of the inserts. Its lazy and it keeps you from actually learning what you should have mastered before you started making you first parts. You are NOT a production shop, you're NOT running thousands of inches a day past tool bits. You have no need for inserts. You have a baby lathe. HSS WILL DO FAR MORE FOR FAR LESS MONEY. But, it requires thinking and learning.