# 5C Collet Drawbar



## Chuck K

I'm planning on making a 5c drawbar for my lathe.  I know the collet thread is 1.238-20.  My question is what size hole do I bore for the threads.  I've googled it and come up with nothing.  Thanks

Chuck


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## raross61

Chuck K said:


> I'm planning on making a 5c drawbar for my lathe.  I know the collet thread is 1.238-20.  My question is what size hole do I bore for the threads.  I've googled it and come up with nothing.  ThanksChuck


Hey I second your question on this one, I too have been trying to figure the major, and minor dimensions, so I can go inside the tube and machine a step for a safe stop spot! It’s easy to get the 1.25” spec's but the guys that did it that way, tell me it works but the collets are pretty loose, on the tube threads!                                                                   Bob in Oregon


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## Chuck K

I was measuring the OD of the threads on my collets today.  I have a hodge podge of collets that I have acquired over the years.  About 90 % of them are hardinge.  I just used a regular mike over the top of the threads.  The hardinge measure about .015 larger than the imports.  Assuming you used the 1.250 threads, I would guess that the hardinge would probably fit alright, but the imports would be real loose. I've made them before and they turned out alright but I would like to start with the correct bore this time. 

Chuck


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## Codered741

The Machinery Handbook will have all of the formulas necessary for calculating the minor and major diameter of this thread.  I was looking at this information the other day, as i too am planning on building a hand-wheel collet closet for my Heavy Ten.  (Once I finish the rebuild)

The thread below has most of the information needed to make the calculations.  But you will need to find the formulas themselves in the Machinery Handbook.  If you don't have one, get one, even an old one.  I find that it is the most used tool in my toolbox, I use it most every day I am in the shop.  I don't have one handy here at work, but ill try to take a photo of the page when I get home.  

http://www.hobby-machinist.com/show...Lathe-Question?p=135771&viewfull=1#post135771

Good luck!

-Cody


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## 4GSR

Machinerys handbook does not have the formulas for 60 deg vee threads.  You have to extrapulate them from given information on threads that are the same pitch but different diameter.  Formulas can only be found in the ASME-ANSI Specification B1.1 for screw threads.  (Maybe an ISO specification by now).

In the down load section, there are several useful references on figuring thread parts including one that I've been using for many years now.

Ken


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## Chuck K

Cody, I have the Machinery Handbook.  I looked in it briefly for 5C collets and didn't find anything.  I guess maybe I need to dig a little deeper.  It seems to me that when I cut threads, the diameter grows somewhat.  That's why I don't want to go with just the major and minor diameters. (not sure which is major or minor when talking about internal threads)  I don't know if I'm explaining this well, but it would seem that I need to bore the hole a bit larger to accommodate the growth in the threads.

Chuck


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## Codered741

The formulas that I am speaking of are for threading in general.  The threads are a standard 60deg thread form, but on a non-standard diameter.  Look in the Threading section, under 60deg sharp threads.  There are a series of measurements and formulas for calculating the thread depth, major and minor diameters, etc, based on the pitch diameter, which in this case is 1.238".  If I had mine handy, I would photograph the page, or give you the page number.  

If you don't find it before I get home, I'll post it.  

-Cody

EDIT:  

The Machinery handbook should also have dimensions for a 5C collet, and various other collets as well.  I was just looking at the page the other day, to determine the angle of the taper.


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## Chuck K

Cody, I won't be able to look at my handbook until tomorrow.  I tried going to the downloads section but I got an error when I tried downloading the threading info.  Probably the laptop I'm using.  I'll try again.


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## 4GSR

Chuck,

Here is a Hardinge drawing for the thread to use with 5C collets.


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## Chuck K

Ken, Thats about as detailed as one could ask for.  I'm surprised Hardinge would put that info out there.

Chuck


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## 4GSR

I hijacked this from another site.  The person that posted it apparently worked for Hardinge or had inside contacts that got him this information.

In some of the older Machinery's handbooks, like the 11 th or 12 th edition, they have a couple of pages devoted to the different collet types and some of the basic dimensions for identifying.

If you dig deep enough on Hardinges website, they used to have some dimensional information available, too.

Ken


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## Codered741

Got the Machinery Handbook out tonight, and found the dimensions for the threads, as well as the 5C collets.  

On Page 1720, 28th ed. Dimensions and relationships of 60deg threads.   



On Pages 945+946, 28th Ed.  Dimensions of standard collets.  






As far as exactly how large you should cut the bore, prior to threading.  It looks like the minor diameter (bore) of the internal threads should be 1.218, prior to threading.  (1.238-(.375*H)*2,  H being .027, the depth of the thread)  I have never had the thread "grow" on any threads that I have machined.  If this is happening, make sure that your bit is sharp , or use a file with emery cloth on it to bring the diameter down.  You may just be experiencing burs that accumulate on the crest of the thread, or the thread is not yet large enough.  

If you choose to feed the tool in with the compound, be sure to compensate for the angle of the tool when calculating depth.  depth * (1/sin(60.5) = adjusted feed number for compound feeding.  This equates to 115% of the depth, for unified standard threads.  So in this case you would need to feed the compound in .031" to get the true depth of .027".  

Good luck, ill be watching closely to see how it goes.  

-Cody


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## Chuck K

Cody, If my calculations are correct, you're saying that the bore should be 1.228.  I'll try that on a scrap piece and see if it works out better.  I used the dimensions Ken posted above.  I bored it 1.1875.  I cut the threads until my hardinge collets threaded in nice and snug.  The import collets fit kind of loose, but I don't have many of them and they will be replaced at some point.  Thanks to all for the input.

Chuck


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## yugami

Bore diameter changes slightly depending on class of fit.  The lower diameter you used is probably closer to the 3B class. 

The basic math is 

Clearance = OD * %ofthread / TPI

Bore ID = OD-Clearance

So at 80% thread engagement you get 1.188


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## Ray C

My favorite handy-dandy formula is:  BoreDiameter = BoltDiameter - 1.15/Pitch.

In your case:  1.238 - 1.15/20 which equals 1.181.  This will give you a 100% engagement so, what you need to do is thread it until you get the correct depth then, take a couple thou off the crest.  Works for me every time.   BTW, the inserts I use have a leading edge that automatically starts trimming the crest off once you reach the proper depth.  Each insert is designed for a particular pitch.  For general purpose work, I just use a very large insert that cuts an 8TPI thread so, in that case, I have to cut the crests off manually because the point is much longer than needed for any thread with a pitch finer than 8.  When I'm doing work to spec, I use the appropriate insert and always end-up with a very high-class (high end of class II usually -almost class III) fit.  The boat propeller shafts I make/refurbish are almost always 16 or 18 TPI class II (if they're US thread).  BTW, class III threads are pain in the butt -way too finicky.  For the most part, I think class III is not for fastening but more for calibrated/threaded measuring instruments and the like...

Ray


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## Codered741

Chuck K said:


> Cody, If my calculations are correct, you're saying that the bore should be 1.228.  I'll try that on a scrap piece and see if it works out better.  I used the dimensions Ken posted above.  I bored it 1.1875.  I cut the threads until my hardinge collets threaded in nice and snug.  The import collets fit kind of loose, but I don't have many of them and they will be replaced at some point.  Thanks to all for the input.
> 
> Chuck



Hey Chuck, 

I forgot to account for the depth on the other side of the thread as well.  The Diameter according to the formula should be 1.218.  Everything else should be the same.  I corrected the formula in the original post.  It now reads, (1.238-(.375*H)*2,  H being .027, the depth of the thread)

Sorry for any confusion.  

It is interesting the 1.1875 bore fit the threads tightly.  Something does not make sense here...  Perhaps the measurement (1.238") is not the pitch diameter?  I am going to do more research.  

-Cody


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## 4GSR

My old ANSI standard (pre-unified system) says nominal diameter- .0541" = bore diameter minimum.  With a tolerance of plus .0054"

Which comes out to 1.199/1.204" bore diameter.

The Newer ANSI Unified system says 

Thread bore diameter =
	Minor diameter, minimum = nominal-1.08253*p
	Minor diameter, maximum = Minor dia. min.+.25*p-(0.40*p^2)

Which comes out to 1.199/1.210 dia. This applies to both class 2 and 3 threads.

The unified system gives more tolerance on the bore diameter.  

I used to know all this by heart 20 years ago when I was involved in writing standards for the company I worked for back then.  Even though I still use it, its now in a Excel spread sheet so I don't have to hand crank calculation anymore.

Ken
Ken


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## Codered741

Ok.  I see where I went wrong.  

It has been too long since the last time that I read a technical drawing, and forgot that thread class size is the major diameter of the thread, not the Pitch diameter.  

So in this case, 1.238" is the diameter of a shaft ready to be turned for External threads.  From there, you would subtract the double depth of the threads, .054", to get the minor diameter of .184". The pitch diameter would be the major diameter minus half the double thread depth.  Or 1.238 - .027 = 1.211.  Therefore, according to the formula, the ID before threading should be 1.191".  The Handbooks' formulas take into account a small flat on the crest, which accounts for the difference in the drawing from Hardinge, and the calculated number.  

This makes much more sense to me.  I apologize if I threw anyone else off track.  

-Cody


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## Ray C

BTW, that formula below also works for tapping a hole but, you need to take that final number, convert it to 64th's and round up to the next whole 64th inch.  Stick the tap in the hole and go for it.  Works every time and the final size will be in-agreement with any standard tapping chart.

Of course, if you're threading on a lathe, you're not worried about breaking a tap so, just bore a hole to the number you derive with the formula, get the boring bar out and start threading until you hit the right thread depth -then, knock off the crest (because they're useless and problematic anyhow).

I don't do as much threaded boring as I do external shafts but, I've done it 10 times more than I can count and it always works.  I derived that little formula myself -and I'll be darned if I remember how but as I recall, it had to do with 1.15 being the reciprocal of the cosine of 30 degrees.  Maybe I'll find the scratch paper I used to sketch it all out and derive that -but I won't bother to derive it again because it just works...


Ray


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## Chuck K

Ray, I bookmarked your formula.  That will save me a lot of time..and guessing.  I've never tried inserts for threading.  I guess when the drawer full of hss bits runs out or my eyes get so bad I can't see to grind them, maybe I'll think about buying some.  Thanks

Chuck


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## Ray C

My eyes (and patience) went down the tubes a long time ago...  Those little inserts are lifesavers in that regard but, I will admit, they're pricey little devils at about 6 bucks each.  Fortunately, they last a very long time.  I used the same tip once for well over a month and that included 22 stainless steel caps almost 2" diameter with 1" of thread length -then I used it on normal steel for a good while after that.  It didn't die until I fell asleep at the switch and didn't yank the lever when I was supposed to... -but then there's 2 more tips (triangular) to go.   Also, they cut at much lower speeds if needed because they're carbide, sharp as razors and have a lot of top rake.  I do so much lathe threading, it's not even funny.  Let me know if you ever need help selecting the right tools and inserts should you decide to go that route some day.


Ray





Chuck K said:


> Ray, I bookmarked your formula.  That will save me a lot of time..and guessing.  I've never tried inserts for threading.  I guess when the drawer full of hss bits runs out or my eyes get so bad I can't see to grind them, maybe I'll think about buying some.  Thanks
> 
> Chuck


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## Ray C

Here's another little tidbit but first, let me mention these are my little tricks that work for me.  There are other ways (probably better at that) to skin the cat so, I make no claim this is the right way of doing things.  I will say though, my threading success rate is well upward of 97%...

First, here's another derivative formula from the first one.  Lets say you have a shaft of the correct diameter that needs threading.  How deep should you go?  Funny you ask...  OptimalThreadDepth = 1.15/(2xPitch).   Now here some caveats.  A) This will give a 100% engagement (which is useless and will never fit due to friction and micro-burrs).  B) There is always a little tool deflection so, actual depth is often not what you dialed in.  C)  The starting point when the bit first makes contact is difficult to really know.

So, if for some reason you want to make a 1/4"-28 thread, take a piece of 1/4" stock, zero the crossfeed and cut until you reach 1.15/56 (equals 0.0205").  Keep in mind that with most thread cutting, a little cold-forming happens too and the diameter of the shaft as measured by reading over the threads will probably be more than what you started with.   Now comes class of fit.  If you want a class III (very tight tolerance fit) lookup the nominal diameter (see link for 1/4-28 3A) which is 0.2500 +/- 0.0000 and trim the OD until it's exact.  -You're done and you probably have a threaded rod that will be to tight for most practical purposes.

Now let's say you want instead a class 2A (more reasonable fit).  Look in the chart and trim the crests until you reach between 0.2500 and 0.2490.  Take out your thread mic and read the pitch and verify it's in the tolerable range for 2A... You'll probably need to dial in a tiny bit and go a little deeper with the threads.  You're done...

This is why it's so important to have a QCTP that is repeatable because in this process, you've had to swap off the toolholder to trim the OD then back to possibly adjust the threads.  Also, I find it tremendously helpful to have a half decent thread mic.  You can do it with wires but, be prepared to be there a while. I did it this way once/twice then bought a thread mic.

I hope this is making sense because it's a lot of words to read but, it's really easy when you think about it.  Everything here also applies to internal boring... Same principles, formulas etc.  Truth is, I don't do as much boring as external threading but, it all works as I've done it many, many times.

Finally, I rarely use dies and always prefer lathe cuts and obviously, for simple threaded holes, I use taps -and taps are available in different H and B (Height, Base) levels to achieve the class (B-rating) you want assuming you've bored the hole to the correct diameter.  If you want any Class III B fit, you need to start with the diameter as specified from the formula from an early post.  (i.e. BoreDiameter = ShaftDiameter - 1.15/Pitch).  To achieve a good staring hole for a given class, use a value of ShaftDiameter in the range for that class.


http://www.engineersedge.com/screw_threads_chart.htm


Now, here's why I use those fancy little inserts.  Look at the picture.  This insert is designed for a particular thread (I think this one was a 13 TPI).  Look at the very edge of my fingernail tip and see the leading cutting edge at the base (widest part) of the cutting edge.  That little edge will start trimming the OD when you hit the right depth.  Take a rod of the nominal diameter for the class fit you want and keep dialing in until you reach the desired diameter.  -You're done!  

I'm not sure if all inserts have this feature but, I specifically went with this brand because I had never seen it before.  Maybe others have this too but the other inserts I used to use, didn't do this.

BTW, that particular insert has been used like crazy it's still sharp as heck and ready to keep going.  You can't see it because of the reflection but that insert has quite a top angle for aggressive and clean cutting.  You can get away with much lower RPM or, use it faster too.




Once again... Caveat Emptor.  These are little tricks and formulas I figured-out myself and seem to work unwaveringly.  Happy threading...


Ray


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## Codered741

Those inserts look pretty cool!  Do they come in other thread patterns?  Like ACME, Metric, Whitworth?

Do you have the manufacturer name/info?

-Cody


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## Ray C

Yep, they come in everything under the sun... Metric, ACME, Whitworth and a few I never even heard of...

They're called "Carmex" brand and they are also the parent company of Iscar.  Here's a random example of that style of insert.  If you order, contact them and ask for a guy named "Avi".  Mention my first name and this website and he might give you a better deals or let you break-up orders and still get quantity prices.

http://www.ebay.com/itm/10-Pcs-Carm...831?pt=LH_DefaultDomain_0&hash=item3cd4b94e97

If you look up Carmex USA and visit their home page, they have a lot of great resources and how to order their products (i.e. naming/sizing conventions).  I like their insert holders too...

Ray






Codered741 said:


> Those inserts look pretty cool!  Do they come in other thread patterns?  Like ACME, Metric, Whitworth?
> 
> Do you have the manufacturer name/info?
> 
> -Cody


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## Ray C

Also, download their catalog http://www.carmexusa.com/pdf/2013-catalog.pdf and also visit the links on the left column on their website.  Lot's of good info about Left and Right hand turning...

Ray


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