M12 thread in stainless

I am currently making an M12x 1,75 drawbar for a milling machine, but have struggled to find any clear guideance as to what should be the turning diameter, prior to using a hand die. The piece of bar I am using is 12mm diameter.

I have measured a M12 bolt and have turned down to 11,65 dia but when I try using a die holder in the tailstock of the lathe the bar friction appears far too great and the bar simply turns in the collet. I appreciate I could use a length of Metric studding but I'm trying to gain some experience of turning and studding would be cheating. (I am using an HSS fixed die, ie no split and am using tapping lubricant) I cannot thread turn it, as my lathe has an imperial lead screw

Any help would be much appreciated.

Regards Pete

11.65mm is quiet a lot under size for cutting an external thread ,so in theory you should be able to comfortable cut the thread.

The problem with stainless steel is it can work harden as its machined ,but in your case I'd say that your die is of poor quality , I'd buy a better quality die but one that is split so that you can adjust the die between cuts .

Making a M12 thread with a die takes much force and it is better to use a chuck than a collet to hold the bar.

Niko.

Hi,

If you have a screwcutting facility, I'd machine cut it if it is in stainless. The problem is that every time the bar slips the die will stop and it will work-harden the steel and its even harder to get it to cut again.

Neil

It would be better if you turned a short length of the Stainless bar to the root dia, about 5mm long and make an angled shoulder for the die to bite on.

If the die is not cutting then both of the other reasons apply from earlier threads.

Do you know the type of Stainless steel?

Clive

Use Mild steel. Stainless is not necessary and is introducing unnecessary complications. MS is not expensive. A better alternative is to use a high carbon steel. I wolu not use Stainless in this application even if it was free.

Best regards

T

If the die is not split it might actually be a dienut, which is not intended to cut a thread, but to clean up existing threads. Either way, cutting a M12 thread by hand with a die is going to take a lot of torque.

Regards,

Andrew

Mark, I know you want to gain experience but cutting a thread on a stainless bar using a die nut is NOT good experience it is a waste of effort.........IMHO.

So if you are intent on making a drawbar from scratch make it from mild steel and get a proper split die., if you cannot screw cut the thread on your machine. Hold the bar in a chuck not a collet. The mild steel will not work harden like SS and will be more than strong enough for your needs.

Alternatively simply use M12 studding and turn and fit a threaded "head" to fit on the other end so that you can tighten the drawbar, and also tap it to release your collet chuck etc. You could, assuming your machine is a current one, simply buy a drawbar. This may sound like sacrilege to some on here but frankly a clever engineer finds ways to reduce work not make life lore complicated.

If you take the "easy option" you can spend more time gaining useful experience on using your machine to make stuff......far more worthwhile, again IMHO.

Given the trouble you are having, I'd suggest threadcutting the M12 onto mild steel rod as others have, or find an M12 bolt, cut the head off, and weld the threaded end to a rod. Reason is, most commercial bolts have a machine rolled thread which is semi work hardened and the grain of the steel has been cold formed rather than ripped away as done in thread cutting. A bolt thread will give a tougher thread that will last longer in drawbar service. This is applicable to homemade clamps and machine parts too.

As to your trouble with the die, the die likely is not sharp enough, you could have a rough piece of gummy stainless stock, or your lead-in could be the wrong angle and maybe the small end is not small enough. For lead- in angle, 20-30 degrees per side works well, and if the end dia is about 0.5 mm smaller than the die's hole you will be sure to get it started as cleanly as possible.

JD

I cannot thread turn it, as my lathe has an imperial lead screw

----

Just use a 35 on the spindle and a 63 on the leadscrew

Your diameter is fine, cut a rough thread on the lathe and finish off with the die

Stainless is tough stuff though, a carbide tool may be your best bet and take off as much as you can so the hss die hasn't got too much work to do

(I've been trying to upload some piccies but this place is a nightmare tonight)

Edited By Ady1 on 28/10/2012 02:37:38

Cromwell can supply a length of High Tensile studding for a couple of Quid, easily turned and fit a Hexagon pinned through one end.

Clive

You really need a fairly heavy die, say 2" split button die, so you can put some real weight into it, and try and take it down in one cut to get round the problem of work hardening. As others have said mild steel is quite addequate, after all it only just gets nipped up. I'v got one that I made by cutting the heads off two bolts, and welding them together, even with my welding its held together for the last twenty years. The other draw bar, a comercial one is quite hard, and is blued, not a pair of rusty bolts, but its just as good, cost two old bolts, time cutting the heads off, welding, put a washer and nut on the top end, all done. Ian S C

I'm doing the ends of a 39 inch square bar at the minit

Cutting most of it on the lathe leaves the die to only finish the job off

This one is finished

This one needs the die to run up it

It takes a bit of figuring out but saves a bucketload of hassle once you suss it out, concentricity is automatic and most of the material(and hard work) is removed on the lathe

You will have additional issues using stainless which is not a user friendly material

You've kind of pushed yourself too far if you haven't done it before, running before you can walk

If I was you I would just buy a length of 12mm threaded rod for a tenner from B+Q

Hi Mark

All the drawbar does is hold the two tapers together. You don't need great strength as you should not pull it up too tight - it's the good fit between the tapers that do the work. You will need it to extract the tapers when you need to change tooling but only a light tap should be needed unless you've really been heavy handed initially. Better still make an extractor as shown on other threads here - Sorry I don't recall which but maybe someone else will remember.

I would use  studding or MS and save my stainless for another day.

Regards

Norman

Edited By NJH on 28/10/2012 12:09:09

Hi all,

Thanks for the multitude of suggestions. It is amazing what you can learn in a short space of time and this makes being a member so worthwhile.

In the end I opted for Jeff’s and Ian’s suggestion of cutting the head off an M12 bolt, but rather than weld it, I turned a spigot on the end and press fitted this into the original piece of 12mm stainless steel bar that I was struggling to thread. I cross-pinned these parts together.

I had already machined the head cap and press fitted this onto the other end of the bar and cross-pinned it. (The result is shown in the photo)

Thanks also to Ady1 for his comments re using my imperial lathe to cut metric threads. I shall be following up on that suggestion, for future projects.

Appreciating that there are many other and quicker ways of making a drawbar, my main aim was to get some practice on the lathe and mill, whilst at the same time making something useful and reasonably aesthetic. The stainless steel was FOC and machined well with carbide tools, but I will avoid it in future, where threads are concerned.

Kind regards

Mark

Mark, that should do the job. Normally a draw bar has a thread at each end, the bottom one is screwed into the tool, the top onehas two nutsthe bottom one is for tensioning the rod, the top one is pinned (it becomes a bolt head), is used for screwing the bottom thread into the tool. There, clear as mud. Ian S C

Hi Mark,

Don't be put off using Stainless in future because of a few difficulties making a M12 thread. I suspect you would have had similar problems cutting the same thread in Mild Steel, anything over about M10 can tend to slip in a chuck when using a die, depending on equipment available. Stainless does indeed have its little foibles but it is not that difficult to work, despite what some would say, and for me the ease of getting a near chrome like finish out weighs any troubles you might get drilling or die-ing. As for straight turning, you hardly notice any difficulties, save maybe having to take smaller cuts than leaded MS.

So, if you don't like rust appearing on something you have just spend your hard won spare time on making, make it from free cutting 303 stainless. Don't, however, ever assume that that nice looking piece of SS is 303, there are some real swines called stainless out there and I suspect that most model engineers are put off using this very useful material by someone in the trade having a joke by giving a newbie a lump of useful looking of unmachineium.

chriStephens

Nice job Mark, looks well done. JD

PS - I second what Chris says about grades of stainless - it is hard to make sure you have the real thing that you want. Dealing with a big commercial steel dealer is a good start. You can do a magnet test at the dealer for 300 series grades - a magnet should not stick to any 300 series stainless. You could take a file with you and if it files easily it is probably machinable. You can check how round it is with a caliper or micrometer, and observe the finish whether ground or rolled, is fit for your use. However, determing whether your stainless is 302,303,304,316 etc is much more difficult - spark tests of all these grades are almost identical, even detailed metallography which is involved and costly, well beyond most home shop builders, will not always ID these grades accurately. Probably best to go to a commercial dealer, ask for a scrap to do a machinability test on, go home and turn it, drill it, etc. if OK go back and buy qty you need. Even with commercial dealers there can be batch to batch differences and mis-identified steel.

Two observations from me which I hope will help you Mark.

Firstly there are as many grades and alloys of Stainless as you can possibly think of. Each having its place in life and engineering. Many of the stockists of small/short ends do not know precisely what they are selling in this respect. Speaking as both an engineer and a motorcycle restorer I have found this out to my cost. Buy from a known dealer who can identify his stainless for you.

Secondly, I am pleased that you have managed to make a tie rod, however as IanSC has pointed out you need to have a thread and lock nut at the "tightening end so that you can secure the shank of your collets etc. What you have made is only an elongated bolt as you have secured the "hammer/mallet" end by pinning. Ideally you need to have a loose collar to enter the end of the spindle and 2 lock nuts to secure the rod when tightened. With you design there is a risk that under some conditions the tie bar could become undone in use, for instance when stopping or reversing a spindle.

Hope this helps.

Michael