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Weird Lathe Question.


Astro_Al
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Right here's something that's been knocking away in the back of my mind for a while.

My lathe has a max run of about 2 foot between the chuck and tailstock. What I'd like to do is work on some bar up to about 8 foot long and up to say 3" in diameter.

The operations are very basic, so the solution needn't be the most precise machine on the planet. I figure I have 2 options.

Find something with a large enough diameter bore through the headstock to take the material, then just do the work in sections until the whole bar is machined (start at one end, work on a couple of feet of bar, release chuck, feed more bar through, re-chuck, work on next section etc etc...). Or... 'Make' some kind of basic lathe (probably cannibalise something ebay-esque for the chuck / motor (needn't be huge), so that I can work the whole bar in one operation. This would need some kind of custom (booty-fab) bedways for a cannibalised tool post, along with associated handwheels etc.

So, anyone know what the best option is? Cheap is nice, as I say it doesn't need to be too accurate. I guess the easiest bet is to find something with a nice big spindle bore, but does that exist on a small-ish lathe?

Cheers, Al.

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jobs tend to get cheaper when theres multiples involved!

Not when they are all slightly different... :rolleyes:

>"At the rate you work it'll be a one-off for at least two years "

Yeah, well, hopefully that'll change in a few months... :ph34r:

>"WTF are you making, or is it a secret off-road weapon?"

I've gone all shy... Hmm wonder why there are no small-ish (i.e. not HUGE) lathes with decent spindle bore diameters???

I'll keep thinking. Al.

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Al,

My 2p

Lathe work Golden rule Number 1 ……………….set your work up so all the machining can be done without moving the work from its datum …………..

You will run into all sorts of trouble …………….. the run out at 2 feet on most lathes that we can afford will be intolerable …….. (mind, I still talking thou’s in the singular here)

Also what speed do you need to run for the machining operation , because 8ft of 3inch bar flopping around is gonna’ make a mess of something. A lathe with a 3 inch headstock clearance will be a little on the large side.

Machines for doing that sort of length with any accuracy are a bit special …………

Maybe you will safe yourself a load of hassle, grief and finance by out sourcing………. You need somewhere that machines boat propshafts ……….. I know that the RNLI in Poole do their own. ;)

:)

Ian

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Al,

You are in the realms of a decent machine shop now, a lathe with a ø3" bore and 8' bed is not that big (typical machine would be a harrison 600), but big enough to be harder to find, you should have a machine shop within reasonable distance to cater for your needs. If they have the bed length, spindle bore is not an issue when using supporting steadies etc. You need somebody who has the bed length perhaps a travelling steady, and a good operator who knows his machine, making (or programming) fine adjustments for the taper that WILL happen without correction.

To do this on a lathe with a 2' bed length is nigh on impossible, as BBC mentions the runout caused by overhanging vibrations etc etc would make it a nightmare and certainly one of the most dangerous things you will ever attempt (its pretty scary when a lathe whips long bar up, Ive been there, done that with a ø4" piece). In short, dont kid yourself, go to an engineeering shop. I have seen "posts" bolted to the floor with a bored tube mounted to centre height, with a slighty larger bore than the diameter of the material being worked to stop vibration and whip, but its crude, desperate and would give poor results.

Of course, Steve Hiatts offer of a 6' bed would almost work (assuming spindle bore is good), you could centre drill each end, then turn one end down, then either using softjaws (bored to suit) or a 4 jaw (and dti) reverse the bar and complete the job, some emery cloth cleaning would disguise any join marks.

(just to annoy you, the machine shop where i did my time would class that type of work as soooooooo small)

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At least it won't take up much workshop space between the vapor-car, vapor-CNC-laser-cutter and vapor-tube-notcher - just as well since the mog axles are as non-vapor as you can get, I think they're made of some sort of German dark-matter.

Who woke him up? LEWIS !!!! :rolleyes:

Honestly, 3 stolen months in the corner of someone's workshop and he's turned into Isambard Kingdom Brunel... ;)

Well, thanks for all your inputs - especially from those who have never used a lathe... :o:rolleyes::D

I'd agree with just about everything written, except that the accuracy of what I need is really low, and it'll be absolutely fine to do either in sections or (hopefully) one end then the other (sorry, that's my fault for not giving any details). If it works out, I'll get my hands on Steve's lathe and give it a whirl.

I still don't understand why they don't put decent spindle bores on smaller lathes - wouldn't it make sense to match the chuck capacity, at least? I guess its a cost thing (bearings?).

Anyway, cheers for the thoughts. Al.

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I still don't understand why they don't put decent spindle bores on smaller lathes - wouldn't it make sense to match the chuck capacity, at least? I guess its a cost thing (bearings?).

Anyway, cheers for the thoughts. Al.

More than likely related, but more probably sales driven, the last time I purchased a lathe for the company(circa 1995), we opted for the big spindle bore version an extra £22,000 on a machine already costing £350,000 :angry:

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Hmm, crazy innit? How much bigger was the bore on that?

I still don't see why 2 or 3 inch bore on a smaller machine like a Colchester or whatever would be prohibitively expensive.

Grrrr...

Anyone got 27 spare fixed / travelling steadies already packed into a box with my name and address written on the front?

What do you mean 'longshot'?

Al.

:)

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(just to annoy you, the machine shop where i did my time would class that type of work as soooooooo small)

As a time served turner i would agree and say sub the job out.

Where i served my apprentiship as a turner in the 70's we had a lathe that i spent some time on, and from memory it was 8' center hight by 65' between centers, at the end of my apprentiship my lathe was a 42" center hight by i think 40' between centers, generally the jobs were in the regon of 35 tons weight and a value of £2M plus when finished.

I have to make do with 8" center hight x 3' between centers now, with flat belt drive to boot, just need to rewire the workshop to get it working again!!!

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