Lathe for a new starter

[Anonymous]

I can't comment directly on the selected lathe, as I've never used one. I have visited Warco to look at milling machines with a mate who was thinking of buying one, not for me though. Here are a few thoughts, make of them what you will:

In theory a 3-phase motor runs more smoothly than a single phase motor, although the difference is unlikely to be apparent on most lathes. if I didn't have a 3-phase supply I'd go for a VFD and 3-phase motor, followed by a BLDC motor. I'd avoid brushed DC motors, I have one on my mill power feed and the brushes are a PITA. One issue with any of the electronic speed controllers is that at low speed the motor is constant torque, not constant power. If turning a large diameter at slow speed it may not be possible to take a decent depth of cut. Gears/belts provide constant power so torque increases as speed decreases, but they are expensive to provide.

I use micrometers for almost all my measurements up to 18". Calipers only get used for rough work. For micrometers an increment of 0.01mm is fine. Trying to measure to a micron is expensive and probably pointless in the average workshop, amateur or professional. Mitutoyo do a digital 0-25mm micrometer with an accuracy of 0.5um; it costs £1980 including VAT. All of my micrometers are secondhand, mostly bought on Ebay.

When I first started out I bought a genuine Dickson toolpost for my lathe, but never fitted it and never will. I prefer the simplicity and better rigidity of the original 4-way toolpost. If using multiple tools for a job I simply keep a set of shims with each tool when swapping. It doesn't take much longer to swap a tool in the 4-way than with a QCTP. Most of my turning is done with four tools; roughing tool, knife tool, parting off blade and boring bar. Of course some jobs require specials, insert and HSS, but the overall number of tools for a given job is still small. Personally I think QCTPs are a waste of money. A common comment on here is that we are amateurs and have the time to take lots of small cuts. So why is it so important to save a few seconds when changing a tool?

I use a Dickson QCTP on my hydraulic copy unit as that is what it came with, but in general I am taking fairly small cuts:

While a tool needs to be on centre height to cut correctly the degree of accuracy needed is sometimes over-stated. I don't have a centre height gauge, I judge the tool neight by eye against a tailstock centre when setting up. Quick 'n' easy and works fine for me.

Andrew

[Mick B1Participant @mickb1]

Tool centre height isn't especially difficult. Despite being a metric lathe, my WM250V appears to have a toolpost slot machined for 1/2" tools.

I find HSS tools that large a bit of a fag to grind, so I use 1/4" square HSS blanks – which appear easily available – supported by a packing shelf made by milling out a 1/4" square step from a 2" length of 1/2"x3/8" flat bar. Sorry about the Imperial dims, but that's the simplest way to express it.

The HSS blanks as bought are normally within a couple of thou of nominal size, I grind whatever profile form I want and put on a top rake so as to intersect the top face with zero or minimal loss of height. I resharpen them in whatever way I can so as to avoid losing that height. Since on knife tools most wear takes place at the very front of the cutting face, I'd usually grind the front end back past the worn area, then extend the side clearance and side rake back along the blank.

That way I have a good range of tools that I can change quickly without messing about with packing.

I have to admit that I hate changing chucks on the WM250V. It's a bit of work, and I use a piece of flat stock between each of the 3 securing nuts and the headstock face to spread the load when unscrewing them in turn to force the chuck off its register. But the real reason I dislike it is because the concentricity of the 3-jaw is so good that I'm worried about trapping some tiny bit of crap between the faces and messing it up.

So I'll only do it if there's no straightforward way to use the 3-jaw, like a valve eccentric for example, or a curved rail for a model carronade trepanned out of a piece of flat bar.

[Chris12Participant @chris12]

About the tools size, how to you decide what size to choose between 6mm to 14mm ? and what is the advantage/disadvantage of using a small/large tool ? (except for the additional grinding required for larger tools, as above)

[Howard LewisParticipant @howardlewis46836]

You can use size of tool that is suitable, as long as the cutting edge can be brought to centre height.

This the important bit, literally!

You can use a full 12 mm shank tool, or even a 1/8" toolbit, on the same machine, as long as the cutting edge is at the correct (centre ) height.

I have used 1/8" toolbits on a lathe capable of swinging 12", but obviously you don't expect to be taking 1/8" a side cuts with it!

I have cut a 4 mm pitch thread, 1.5 mm deep, with a 1/8" diameter toolbit, for a particular purpose, but not in one pass.

My parting tool is 3/4" and inverted in the rear toolpost, but the toolpost was made so that the holder would bring the cutting edge to centre height.

The larger the shank of the tool, or the larger the size of the toolbit, the stronger and more rigid it will be and within the capability of the machine, will take larger cuts. (This does not mean trying to take 3/8" a side cuts with a 350 watt mini lathe! )

[Clive Brown 1Participant @clivebrown1]

Posted by Chris12 on 07/08/2022 17:56:07:

About the tools size, how to you decide what size to choose between 6mm to 14mm ? and what is the advantage/disadvantage of using a small/large tool ? (except for the additional grinding required for larger tools, as above)

The larger tool sizes might add a smidgen of rigidity but really of little consequence for most home machining. For the normal run of model engine making, 6mm square HSS is perfectly adequate. I've owned a 5" Boxford for decades and virtually all my HSS useage, other than parting off has been with 1/4" sq. The largest that I have is 3/8" sq. and that is usually used only if large lumps of steel needs to be tackled. Don't under-estimate the benefit of easier/quicker grinding, especially when a profiled tool shape is required.

I heartily second the comment about ease of changing chucks which is one of the features that I value with the Boxford with its screwed mandrel nose. A swap-over takes just seconds. In a busy working session I might do that 2 or 3 times and the older I get, the more that such chores discourage me. Wish I'd got room for a 2nd. lathe!

Edited By Clive Brown 1 on 07/08/2022 20:12:52

[Howard LewisParticipant @howardlewis46836]

If you have flange mounted chuck, it is easy to drop the nuts (M6 on a mini lathe)

An antipodean contributor to MEW, called Danny M2Z, came up with an amazingly simple solution.

It is merely a bit of thin steel, (I used a bit of steel banding ) with two cuts along it, parallel and 6 mm apart, with the central tongue levered up, and the last 6 mm sharpened to a 90 degree point before being bent downwards by 90 degrees.

Once the nut has been slackened slightly the Widget is inserted under the nut, so that the pointed tongue will enter the nut when it is slackened.

Eventually, the nut leaves the stud, but is trapped between the tongue and the main part of the strip. In this way it can be removed, or replaced with minimal chance of it falling whilst the spanner is on it.

There is no reason why a bigger version could not be made for larger sizes of hardware.

Howard,

[Howard LewisParticipant @howardlewis46836]

The thicker the tool, the stiffer it is.

A 12 mm square tool shank will be 8 times stiffer than a 6 mm square, since stiffness is proportional to the cube of the depth

But a 1/8" toolbit can be mounted in a 1/2" square tool holder, to increase stiffness and rigidity..

A 3/4" deep, 3/32" wide, parting tool is very stiff vertically, but weak laterally so will flex sideways, if the front face is not square to the lathe axis, and fed hard..

What ever size tool is used, overhang should be minimal, to reduce the bending moment applied to the tool shank.

Which is why boring tools, usually having a long overhang for deep bores, need to have repeated "spring cuts" taken, without any changes to the machine setting, until they cease removing metal..

Howard

[Chris12Participant @chris12]

I've been looking a bit at the chucks and methods of fitting on the spindle, and it seems it's going to be flange fitting. Cam lock versions seem to be for bigger lathes, or at least rarer on import lathe. And not sure the conversion can be made afterwards.

This is the problem when buying machines : there is always a small improvement on the next level machine. You start by thinking to spend 1,000 £ and you end up at 5,000 £

(had the same issue with my woodworking machines/tools)

[NealebParticipant @nealeb]

"He who spends too little on a tool regrets it every time he uses it. He who spends too much forgets it the first time he uses it."

More than a grain of truth in that but we do have to draw the line somewhere! It's why I bought an elderly English toolroom lathe rather than a similar price new Chinese machine (plus I got a cabinet full of useful accessories with it) but frankly it was a close-run thing. Not always an easy decision.

[JasonBModerator @jasonb]

My WM280 and the Emco before that use flange mounting and I've not really found it a problem over 30yrs of use. It's good practice to put a piece of board on the lathe bed when changing chucks so you won't do damage if you drop the chuck, this also serves to catch the odd dropped nut.

I can change a chuck in a couple of mins max and with a bit of thinking ahead you can avoid too much changing over such as working on two parts of a model at once so you can do the 4-jaw work for both at the same time rather than changing chucks for each.

If you want to go down the carbide route then 8 or 10mm holders will be quite adequate and usually take the smaller size inserts, once you get to 12mm and above the insert size starts to go up as does the cost.

The only real time a larger cross section tool will have an advantage is if you have some odd set up that requires excessive overhang though reducing depth of cut can go some way to easing that.

6mm HSS tooling should be as big as you need to go on that lathe, I seldom use larger on my 280 and at a push can take a 1/4" deep cut (half inch off diameter) with it chatter free and that's using a QCTP

[Chris12Participant @chris12]

Many thanks all for your inputs and suggestions, those have been very helpful. I hope to have the lathe by the end of the year, and be able to share my adventures on the forum !

[Ron LadenParticipant @ronladen17547]

On my Warco 918 which is a similar size and power to the 250 inverter type I use mainly insert tooling with 8 mm holders, my boring bars and parting tools (rear tool post) I also use insert tooling. I do use some HSS for making up form tooling etc but I would recommend carbide for most general work and 8mm holders are fine on this size of machine. Dont worry about the rigidity of the tooling itself thats not where the problem is, its the overall rigidity in the machine which obviously is nothing like larger industrial machines but for what we do its fine.

Mentioning a rear tool post for parting off that is something to consider further down the line but the 250 comes with a T slotted cross slide so you could buy or make your own rear post which from my experience with my mini lathe and now the 918 transforms parting off from a dread to a pleasure to do and the powered cross feed on the 250 is a bonus for this.

My two penneth anyway.

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