Turning small diameter

[Cogsy]

Hi all,

I'm new to machining and I thought I'd better ask this question before I go ahead and hurt myself or break something

I have some 5mm (~0.195") bar that I want to turn down to 3mm (~0.118") for a length of 66mm (~2.60"). I only have a dead centre and I'm wondering if I face and centre drill the bar, then put the dead centre in the end, will I be able to safely turn down to that diameter over that length, if I take shallow cuts? Or will it deflect, turn into an egg shape, rip out of the dead centre and attack me?

I appreciate your help.

Al.

 

[metaltrades01]

Hi Cogsy, It'll attack you. You need to use a travelling steady, with a little bit of grease on the steady guides. and a v small radius tool (minimal contact area of the tool on the job), fine cut's with a slow feed

 

[Cogsy]

Thanks for that, I had a suspicion it might get nasty. It was my next job for the night but my wife called me in for dinner so I'm glad I didn't try. I only thought of the possible problems while I was eating.

I don't yet have any steadies so I guess I'll have to move on with something else until I can afford to get some, or possibly I can find some 3mm rod somewhere, which would solve the issue too.

Cheers,
Al.

 

[lensman57]

Hi,

66 mm length of a 5 mm bar is a tricky one. If you have a collet holder use it in preferrance to the chuck. I wouldn't bother with center drilling at all, it weakens the rod even more.

There are a couple of methodes you could use.

1- Allow only 10mm of the rod to extend beyond the chuck or the collet, use a super sharp HSS tool not carbide, carbide does not cut like HSS and puts a lot of pressure on the work piece increasing the chances of it deforming under presurre.

2- Face and cut the first 10 mm by doing as least a number of cuts as possible. Remember a 5 mm rod is a lot stiffer than 3.5 mm if your lathe could manage it just do it in one cut. If not you may have to do a trial and error to find the best combination of depth of cuts but as the diameter gets smaller the rod weakens, that is why I'd do it with one or at max two passes . keep track of the position of the cross slide dial or better still a dro if you have one to avoid the back lash problem.

3- Extend the rod a further 8~10 mm and repeat.

The other method is to use a travelling steady , this could be the fastest way but the results are sometimes unpredictable.

I have also once made a special "travelling steady" by drilling and reaming a piece of brass to the size of the rod I am cutting in you case 5 mm, and mounting this jig at exactly the center height so the rod passes through this hole at just ahead of the cutting tool and finishing the job in just one pass, if you wish to make more than one pass then you'd have to make different jigs for each diameter, in all I'd rather use the first methode.

Regards,

A.G

 

[gus]

Hi Cogsy.
You can make your own fixed steady for a song.Took four hours to make mine.
Long unsupported bars will climb over the tool bit.A moving Steady is a must for long jobs.
I have no requirement to make a Moving Steady.

Foto attached. I had a spare hollow shaft disc.

 

[Cogsy]

Thanks lensman, I shall try your method tomorrow. I never would have thought of doing it in short lengths, even though the last part I made was a 14mm long piece of this same stock, turned down to 2mm. I did that at 0.050mm per pass and it worked, I just assumed small cuts would be better.

Gus, thanks for the photo, but songs must be expensive in your part of the world, that piece of brass is probably worth more than my lathe . I will be nice to the wife until she lets me buy some steadies though.

Thanks for all the help, I'm confident I'll get it sorted tomorrow.

Cheers,
Al.

 

[dreeves]

Do a search for a box tool. A box tool holds the dia so so the cutter cant push the part awar from the cutter. It works somewhat like a follow rest by it is all at the cutter.

Dave

 

[Sk8Ter]

Do a search for a box tool. A box tool holds the dia so so the cutter cant push the part awar from the cutter. It works somewhat like a follow rest by it is all at the cutter.

Dave

Hey Dave where can i buy one of these?

Lawrence

 

[gus]

Thanks lensman, I shall try your method tomorrow. I never would have thought of doing it in short lengths, even though the last part I made was a 14mm long piece of this same stock, turned down to 2mm. I did that at 0.050mm per pass and it worked, I just assumed small cuts would be better.

Gus, thanks for the photo, but songs must be expensive in your part of the world, that piece of brass is probably worth more than my lathe . I will be nice to the wife until she lets me buy some steadies though.

Thanks for all the help, I'm confident I'll get it sorted tomorrow.

Cheers,
Al.

A search into my files.I file completed projects and cost.
OK the Bronze Brass Hollow Shaft Disc cost me S$10 or US$7.98. The cheapest and nastiest China made steady cost US$54.Box tool is good idea but tough to DIY.
There are stockists here that will cut bars to custom length for an extra fee.

There are some jobs which calls for a particular tool or aid.I did try avoid building steady but on serious thought I could get killed or wreck the lathe and chuck.

 

[Sshire]

Here you go
http://www.homemodelenginemachinist.com/f26/turning-small-diameter-16948/

 

[tel]

Thanks Stan, I was just trying to find those pics to re-post 'em!

And heres's a bit of 1/8" taken down to 1/16"

 

[metaltrades01]

Thanks Stan, I was just trying to find those pics to re-post 'em!

And heres's a bit of 1/8" taken down to 1/16"

Brilliant idea Tel,
Are they commercially available? ....from anywhere else other than the Myford sales place, in the other thread? which say's unavailable (I have just emailed them to ask if you'll be back in stock).
Otherwise I guess make one in the mill with provision for little bush's to fit in the back, that you individually ream to size to suit the original diameter you want to machine.

 

[tel]

Don't know if there are any other commercial ones around, tho' I dare say there are. Things like that are simplicity itself to make - that one was done years ago, before I had a mill, all the milling was done in the lathe.

The other disadvantage of buying things like this are that you are buying what the manufacturer thinks you want/need. Making it yourself give you the opportunity to get it exactly how you want it.

 

[lensman57]

Thanks lensman, I shall try your method tomorrow. I never would have thought of doing it in short lengths, even though the last part I made was a 14mm long piece of this same stock, turned down to 2mm. I did that at 0.050mm per pass and it worked, I just assumed small cuts would be better.

Gus, thanks for the photo, but songs must be expensive in your part of the world, that piece of brass is probably worth more than my lathe . I will be nice to the wife until she lets me buy some steadies though.

Thanks for all the help, I'm confident I'll get it sorted tomorrow.

Cheers,
Al.

Hi,

Good luck, just one point, if you are going to use the chuck then try not to rotate the rod while pulling it out and allowing the jaws to clamp on the same spot, this will decrease the chance of the chuck run out ruining the concentricity of the chuck and work piece you are turning.

Regards,

A.G

 

[wackyvorlon]

Is there a compelling reason why you can't just use 3mm drill rod?

 

[metaltrades01]

Hi Tel,
I just got a reply to my email from Chronos about these tool holders...
Small Diameter Turning Tool SDTT for Myford Lathes - SORRY OUT OF STOCK (Ref: XC10....)


[email protected]
Hi
Many thanks for the email
Yes they are on order with the factory
Mark

 

[Cogsy]

Thanks for all the help everyone. I did get it done, it's a useable part but far from perfect.

I hadn't read the post about not turning the stock in the chuck when I extended it, so concenticity was an issue. Because of this, when I got to the 50mm mark, I was scared the wobble would cause a massive bend, so I had to spin the rod around and work from the other end and deflection became a real issue. Luckily, only the 2 ends will be visible in the finished engine so the blemishes will only be seen by me .

I'll definitely be building an approximation of your tool Tel, thanks for that, and thanks for the link Stan.

Wackyvorlon - I couldn't use 3mm drill rod because I didn't have any and it's hard for me to get small bits, and I really wanted to see if I could .

Luckily, I've been having more success with the other parts I'm making!

Cheers,
Al.

 

[Sk8Ter]

if there is any interest i am going to make some for the guys...

cost? I have no idea let me make one....I have some 12L coming




Lawrence

 

[gus]

Is there a compelling reason why you can't just use 3mm drill rod?

You are correct.

If you really need a 3mm or 4mm shaft ,why not buy from stockist.

Here in Singapore,we are fortunate 3,3.5,4.0,4.5mm rods and 1/16,1/8,3/16
etc steel/brass rods are available.

I would change design to use rods avalable rather than turning down from a larger diameter rod. If drawing calls for a step shaft like 6mm/3mm,I would have no choice but I may work around.

 

[tel]

Welding electrodes are a good source of small rod as well - just knock the flux off with a small hammer and give 'em a polish with fineish W&D - they are held surprisingly true to size.