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Author Topic: cutting threads  (Read 9674 times)

portside II

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cutting threads
« on: November 05, 2008, 03:37:21 AM »

heres on for the enginers out there ,
I have been making my own prop shafts and tubes for a while now mostly in M4 ,but i have made a few in M5 threads that is .
Is there a standard thread as when i cut a thread on the shaft in M5 and run a M5 nut up it i get a bind after about 1 and a half length's of the nut ,this is so bad that i have broken the shaft trying to remove the nut.
I have run a M5 tap through the nut and thats ok , both the tap and die are M5x0.8 .
Any ideas ??
daz
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Reade Models

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Re: cutting threads
« Reply #1 on: November 05, 2008, 07:49:46 AM »

It sounds like the pitch of the thread on the die and that on the nut are slightly different (number of teeth per centimetre).  This would account for the nut binding as you run it up the newly cut thread.

I suggest you try to establish the number of threads per centimetre and on both die and nuts and make sure they are the same - buy new ones if necessary?

Malc


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Garabaldy

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Re: cutting threads
« Reply #2 on: November 05, 2008, 08:24:22 AM »

the only thing i can think of to add to that is to get a set of these - http://www.axminster.co.uk/product.asp?pf_id=23483&src=froogle  Obviously you can only check the pitch on a male thread but if you bought the nut as standard part then it SHOULD be ok.  Have you tried putting the nut over somthing else which is m5?

Ive had problems with threads before.  The nut holding my prop shaft in had been tapped so poorly that when it went onto the male thread it wasnt mating up concentricly so when the shaft had any sort of RPM on it there was huge amounts of vibration.  Fixed now though  :}
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wideawake

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Re: cutting threads
« Reply #3 on: November 05, 2008, 08:34:13 AM »

My first thought was that the tap and die were of different thread pitches.  there are two standard pitches for each metric diameter.  However you say that both are marked 0.8 pitch.   In that case my next thought is that the core diameter of the thread you cut on the shaft is a bit big.   I don't mean the 5mm but the diameter at the root of the thread after cutting.   Assuming that the die you're using is a split one and the die holder has an adjusting screw then slacken the adjusting screw so that the die closes up a little and run it down the thread again until the nut runs freely.

HTH

Guy

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andrewh

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Re: cutting threads
« Reply #4 on: November 05, 2008, 08:43:34 AM »

Portside
I learned this year that there are in fact two series of metric threads, coarse and fine, so describing a thread as M5 doesn't say which it is.  M5 x 0.8 describes it completely.  (IF it of interest M5x0.8 is metric coarse thread, and if you just say M5 with no pitch ; coarse is implied)

I suspect that you have been tapping the shaft perfectly correctly  - for the first cut :}
Just as there are (should be) three taps in a set, the die nut requires three passes to make the full thread depth.
You are using a tapping compound or  grease?
The die nut is split, isn't it? and fits in the tapping handle with the split next to a pointed screw.  There should also be one or two screws close to the tapered screw that enable you to close the die nut a bit.  
So the first cut is taken with the die nut held open by the pointed screw, the second with the pointed screw backed out
and the third with enough pressure from one of the closiing screws to make a thread which is a good fit in the nut of your choice
If John (bogstandard) is reading this - he is both an expert and a wonderful communicator- he would help far more clearly than me :}

andrew

  
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bogstandard

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Re: cutting threads
« Reply #5 on: November 05, 2008, 09:22:26 AM »

Daz,

Looks like the others have nailed the type of thread and getting it to size, but there is just one little thing missing.

But first, if you do have an adjustable die, you gradually reduce the size of the thread diameter until the nut just goes onto the newly cut thread, but not all the way to the end. If you adjust down until the nut screws all the way up the thread, the first part of the thread will be very loose, to such an extent, if the nut is tightened when on that area, the thread is liable to strip. If you are using a non adjustable die nut (the type normally sold cheaply on markets) you are stuck with the size you have, but this little tip just might get the job done.

If you look at my little crap-o-cad sketch, I hope it will explain a problem with using normal dies to cut a thread.

Pic 1 shows that the leading edge of the die cutting bit is usually tapered to allow it to start cutting the rod easily.

Pic 2 shows what is produced. A tapered thread towards the end of the cut.

Pic 3 shows the little tip, turn the die around. If it is in a dieholder, the holder should have hole in the back to allow you just to flip it over without altering the die compression settings, or if using the die nut, again, just flip it over and start the thread using the back of the die.

Pic 4 is what should happen. The narrower part and non tapered cutting edge (now at the right size for the thread), should just skim off the taper on the shaft and leave you with a completely parallel thread.

Cutting lubricant MUST be used. If you haven't got the correct cutting oil, try a bit of engine oil, or lard (very similar to the old fashioned tallow).
The cutting action should be, one full turn forwards, one quarter back, then another full turn then a quarter back. This action releases the chips that are forming and stops them digging into the already formed thread and damaging it.

I hope this helps with your problem.

John

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andrewh

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Re: cutting threads
« Reply #6 on: November 05, 2008, 09:42:06 AM »

John

You have the same CAD package as me!

only mine is left-handed
andrew
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portside II

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Re: cutting threads
« Reply #7 on: November 06, 2008, 12:43:13 AM »

You guys are genuie (i think thats the correct word for more than one genius) :-)) .
John i didn't know there were two sides to a die  :-) , so is the tapered side the one with the stamped letters ,etc ? , the die is a solid one with no cut for adjustment but not from a set i bought both the tap and die a few years back from a liquidation sale with a number of other items , they were still in their packs with prices on nearly 25. each.
Like i said the nut runs on the tap ok so it must be that i am not cutting the thread with the die fully ,i will do some more cutting and see what happens .
On a simular thing ,i was looking for a die to cut threads same as the ones you find on clevis rods , and ideas of the size ?.
daz
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Proteus

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Re: cutting threads
« Reply #8 on: November 06, 2008, 01:30:10 AM »

I use radioactive rods and use a dia marked   2 X .4 and they fit the clevisses spot on for me ..

 
http://www.jperkinsdistribution.co.uk/list.php?ExpandRef=F429&subcat=3&cat=Dubro&Navmain=Accessories#F429

they say they are 4.40   http://www.shopatron.com/index/pg=1/101.0.5161.5168.0.0.0


Proteus
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bogstandard

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Re: cutting threads
« Reply #9 on: November 06, 2008, 02:36:31 AM »

Daz,

My sketch shows it very exaggerated for description purposes. The tapered entry point is usually on the side with the lettering on.


John
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boatmadman

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Re: cutting threads
« Reply #10 on: November 06, 2008, 05:43:57 PM »

I use radioactive rods

Proteus


Arent they a bit 'hot'?
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Circlip

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Re: cutting threads
« Reply #11 on: November 06, 2008, 06:32:46 PM »

You haven't mentioned what material you're using for the shafts and nuts? If it's Stainless and Stainless beware of "Galling" <:(
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portside II

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Re: cutting threads
« Reply #12 on: November 07, 2008, 12:52:22 AM »

Circlip
Yeah the steel for the shafts is from a batch i bought years ago ,i have no idea what the grade is probably mild steel  thats about all i know apart from it withstands rusting  .
The nuts are from a box marked M5  .
Proteus
i have used the rods from radioactive when i used to crash planes and i still have a load of clevises left over from the bits , 2x.4 is that a metric size , and is 4.40 a BS size equivalent.
daz
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Proteus

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Re: cutting threads
« Reply #13 on: November 07, 2008, 07:00:00 AM »

the 2 x .4 is Metric the 4,40 is an American Jobey that I never been able to understand , maybee the Bogster (Bogstandard) can enlighten us . as he has a wealth of info and build the most amazing model engines.

Proteus
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hopeitfloats

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Re: cutting threads
« Reply #14 on: November 07, 2008, 07:40:43 AM »

that is a strange problem daz. standard 5mm threads are .8 and .9 with .8 being the more common. i have done heaps of 5mm threading in mild and stainless steel without major problems but some grades of stainless can sort of jam the dienut when screwing it on or off and this causes galling as said by circlip. it more or less leaves a rough edge on the thread which can jam the nut. i usually clean it up with a thread file but i  would guess you dont own one. well worth buying if you do a lot because the metric  version covers practically every thread you are likely to use from very fine to very course.
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bogstandard

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Re: cutting threads
« Reply #15 on: November 07, 2008, 07:54:31 AM »

Proteus,

I am no expert on thread sizes, I am just like all the other model engineers, I either use a Zeus book or refer to a chart. I used to use mainly BA, but have now swapped over to metric, with the occasional UNF or UNC. I buy taps and dies as required, Usually from Tracy Tools.

http://www.tracytools.com/index.htm

Usual disclaimer on that one.

Metric threads can be a nightmare at times, there are so many different standards produced for each type of use ie instrument makers would have a different standard to engineering. But in our world there are basically only two, metric coarse (normal standard) and metric fine. The only ever time I have used metric fine was when I cut 4.5mm for fitting Ronson gas valves into a rechargeable gas tank.

Going from experience over many years in model boating, if you buy clevises, you should also buy the matching rods that go with them. It all depends where they were manufactured. If on the Continental Europe, they will almsot certainly be 2mm x 0.4 (standard metric coarse), if they have been imported from the US, 4.40 is a standard unified coarse thread.

But being a cheapskate, I used to use stainless bike spokes and screw them into the plastic clevises, don't know the exact size, but I reckon by now they must now have changed over to metric.

Here are a couple of antique bike spoke machines that I rescued.





They don't cut threads, but roll them onto a soft iron wire. They don't have the rigidity or strength to roll them onto stainless.

I was going to attach a threading chart, but because of the fine print it is too large to add for the given resolution. But a quick search on the net for threading charts usually comes up trumps.

John
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portside II

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Re: cutting threads
« Reply #16 on: November 07, 2008, 09:33:45 AM »

Thats a good idea ,using spokes  i didn't think they were the same size , i will have to be picking up the old wheels dumped at the side of the road from now on.
that site is well worth a look as their prices are a lot better that my local ,i was going to buy a new M5 die but they wanted over 30. where as tracey tools only want 3.00 .
They also do the thread cleaning tool so i think one of them will also be on the order list.
daz
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Captain Povey

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Re: cutting threads
« Reply #17 on: November 07, 2008, 10:57:44 AM »

The other thread problem you will encounter is when you try to fit a turned or cut thread to a moulded one. This is because most cheap mouldings will use thread cores that have not been temperature shrink compensated. So the moulded part ends up with a thread pitch that is smaller than the cut one. Graham.
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bogstandard

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Re: cutting threads
« Reply #18 on: November 07, 2008, 12:35:25 PM »

Daz,

Be careful in what you buy, Tracy Tools invariable show prices for carbon taps and dies, HSS ones are double the price of carbon.

I use carbon on non ferrous as they are really sharp and cut a wonderful thread, but on harder materials they don't keep their edge as long as HSS ones, and they are rather brittle, so you shouldn't force them.
I actually have full sets of carbon from them in UNC, UNF, and all their ME range, plus a load of one offs, and have never found fault with them in all the years I have had them, and have only ever had to replace one, about two months ago, I was heavy handed with a die, and it snapped in half. I had fitted it into the next sized up holder to make a special oversized replacement for a chappie, and I tightened and expanded it too far. That what comes of having hands like a gorilla and the feelings of a brick wall.


John
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omra85

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Re: cutting threads
« Reply #19 on: November 07, 2008, 12:45:02 PM »

Daz
Don't go kerb crawling looking for old bikes - people may get the wrong idea  O0
Pop into your local cycle repair shop (or even Halfords) and ask if they have any old stainless spokes (any length but the longer the better).
You should be rewarded with a handful for very little money. The ends have a nice M2 (ish) thread which screws into the plastic clevises a treat. You can cut them and use the other end with the bend in, through a 2mm hole in your servo horn. Cut to appropriate length and join with a joiner (the brass bit and screws from the inside of a terminal strip work well). You now have a fully adjustable linkage  :-))

With regards tapping and die cutting, always try to get the split dies so you can adjust to your needs, can even compensate for a BIT of wear when you've been working with stainless.
If threading soft stuff, ie brass or aly, WD40 is a cheap lubricant if you don't have cutting oil. NEVER tap aluminium 'dry' - you'll end up with a hole like a bucket!
Taps come in different types - use a "taper" or "second cut" to start a thread off as they have a longer taper (no  :o) to start the thread gently, then use a "plug" tap if threading to the bottom of a hole (unnecessary when tapping right through the material).
Danny
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Circlip

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Re: cutting threads
« Reply #20 on: November 08, 2008, 09:33:46 AM »

I used the term Galling to describe the ability of Stainless to weld itself together if threaded parts are assembled without a lubricant(Copperslip is good). This can occur despite the threads being cut perfectly cleanly, yes, I found out the hard way, M12 bolt and nut.  :embarrassed:
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portside II

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Re: cutting threads
« Reply #21 on: November 08, 2008, 09:25:22 PM »

Thanks lad's ,
I have learned as lot from this discission and wil probably learn more asking the right questions whem i come across the problems .
Regarding bike spokes ,this has brought me to look at the other bits of the bike wheel ,mainly the hub .
If you take a front wheel hub make a mount and bolt it down onto your tug hull it looks like a drum winch ,not to wind the tow line round but to act as a roller ,looks prety good to me  :-)) .
daz
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portside II

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Re: cutting threads
« Reply #22 on: January 30, 2009, 09:28:32 PM »

Oh well back on the thread subject , i have still not sorted out my problem but i may have found what the origin of the problem is  O0 .
In the workshop tonight i was cutting a new shaft for an 8 foot tanker and encountered the thread problem , remembering i hve a thread gauge i thought i would use it .
And there was the answer  :} T.P.I. :
M5 X 08 TAP 32 TPI
M5 X 08  DIE 28 TPI
How is this so there are no markings on either the tap or the die but they cut different .HELP!
daz
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Shipmate60

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Re: cutting threads
« Reply #23 on: January 30, 2009, 10:41:02 PM »

Portside,
Cut a nut in half and check what you have, 28 or 32.
Buy the corresponding tap or die!!

Bob
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derekwarner

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Re: cutting threads
« Reply #24 on: January 30, 2009, 11:11:44 PM »

Hi all......I think we are off the track here........

Metric threads are expressed as diameter x a % or ratio of an increment....the millimeter [mm] pitch.......trying to consider teeth per inch [TPI] is like trying to fit a square Imperial egg into a Metric round egg ring  >>:-(

Let's look.......

25.4 divided by 32 [TPI] = 0.793 mm pitch
25.4 divided by 28 [TPI] = 0.907 mm pitch

I suggest neither of the above are correct as the suspect thread form is M5 x 0.8 mm pitch

Just to confuse %% ......the famed BA [British Association] thread form is actually based on hard METRIC units of diameter to ratio of pitch....please re-read I am not saying whole numbers but hard units

Just to confuse even more  %% %% %%....certain German metric thread form [pitches] are different to those used by the French and also the Japanese....... :o

As bogstandard says......that little Yellow & Black covered Zuess book is good........but it does not cover some of the jewelers fine threads ........

So.... portside II.....put the thread gauge back in the packet & determine which component you need to throw away........... :-)) Derek
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