Q: How to slice off very short lengths of metal tubing?

[mmagliaro]

Ummmm... yeah... what he said.   


EDIT>>>  Not "Difco"... I meant "Dedeco", supplier of dental tools (and thin cut-off wheels)
I actually found mine somewhere else a bit cheaper.  They are only .015" thick (Dremel's "thin" are .025").
That's not nearly the thinnest they sell at Dedeco, but .015 makes a huge difference over .025
I get them from a place called "Ace's Abrasives", and he does have them as thin as .009".
<<< END EDIT

Seriously, narrowminded, what you describe about making your own cutting tools is pretty much what I do.
I have some of those HSS tool "blanks" you can get online, on eBay, at Micromark, almost anywhere.  They
are pretty cheap if you find a good deal.  I use a Dremel with a Difco   Dedeco cutting disk (it's thinner and smoother than
the rough-hewn Dremel variety).  That let's me cut away from the edge I'm trying to make, so I can fade the
steel away from the cutting edge on all sides (just like you recommended!)

Occasionally, I dress off the edge again with the disk when it starts to lose its sharpness.

The truth is (and take that with a grain of salt, since I'm such a machining newbie)... the machining we are going
for these models is pretty crude compared to what a real machinist with top-grade mills and machines can do.
Those folks talk about "tenths"... LOL!   Nothing I ever do will be down in the 10-thousandths-of-an-inch world
for accuracy.  If I get things to within a few thousandths, I'm thrilled.

[Chris333]

So I was just playing with the lathe. How do I mount a regular chuck in place of the 3-jaw chuck? Do I need a whole new tapered head stock that can use a draw screw?

This is what I have now:
http://www.taigtools.com/c1050.html

OK it looks like I need this:
http://www.taigtools.com/c1140.html

I put new "soft" jaws on my 3-jaw chuck and for some reason I can't get them centered.

[narrowminded]

So I was just playing with the lathe. How do I mount a regular chuck in place of the 3-jaw chuck? Do I need a whole new tapered head stock that can use a draw screw?

This is what I have now:
http://www.taigtools.com/c1050.html

OK it looks like I need this:
http://www.taigtools.com/c1140.html

In the vernacular, that's a "drill chuck" as opposed to a "lathe chuck".  It looks like it is what you need.  A collet is the typical way to hold mills both for grip and also for concentricity but that can be fudged when using very small mills, as these are, and if the chuck you're using is running particularly true.  One off's, coax it in with care and you can get away with it.  If you were trying to push a 1/2" end mill at a 1/2" deep cut, I'd say emphatically, don't even think about it in a drill chuck.

I put new "soft" jaws on my 3-jaw chuck and for some reason I can't get them centered.

When you say "centered" do you mean within a few thousandths or are you talking errors you can measure with a yard stick?  I ask because a brief look at the literature suggests that a few thousandths seems to be normal for this machine with aluminum jaws and they need to be cut on your machine to true them up to your machine.  Once trued, they should remain good on your machine for a long time.  But if they are WAY out, that could just be the assembly. 

 A 3 jaw will close based on a scroll within the chuck that rotates, moving the jaws in unison towards center.  That scroll will be visible in the individual jaw guide openings.  The jaws are typically numbered, stamped in the end.  As such, they need to be installed in the chuck in the proper sequence, that which they were assembled and trued to.  Missing the sequence or a scroll step with just one jaw has the jaws either one full scroll step out, or if just out of sequence, it might be one third of a step which will still be measured in fractions of an inch and visibly WAY out of true.  To assemble, you start with the number one jaw, turn the scroll backwards so that it's pushing the jaw out until it passes the scroll start (like a screw thread but on one plane, not radial around the screw) and then when it passes and drops in, you start towards the closed direction, get just far enough to engage the scroll teeth in the jaw teeth, the jaw now captured by the scroll, and then insert #2.  Advance the scroll towards closed until number two is just captured, contained, and then repeat for #3 jaw.  That should be it.

To true soft jaws you place a round, shallow/ thin piece of material deep in the jaws and clamp on it, sufficient to stabilize the jaws, leaving the bulk of the jaws' gripping face exposed/ hanging out.  It is that overhanging part of the jaw that you then bore just until you are cutting on all jaws.  They are now trued to the machine.  If the jaws have steps for various diameters and the chuck is to be used universally, not for a specific job, you would repeat this step for each step until all are trued.  If they have "outside" steps for gripping internally, those steps should also be cut externally so that all gripping faces are trued.  The various steps may all be cut at the same time with the same stabilizing slug in place but often swing constraints will prevent that.  In that event, finish the sets you can access and then use an appropriate size slug for the steps left. That's it.  If the jaws aren't already numbered, now would be a good time to do that.  As you wind them out and get near the end of travel, start to move a little and then tug on the jaws so that you find the first to disengage from the chuck scroll.  That one will be #3.  A little more, then that one will be #2, and finally #1.  Then they assemble as #1 first, etc.  With the jaws now removed, by hand or in the mill, cut away the small slug left where the stabilizing slug was, preventing cutting at that point. 

The diameter of the stabilizing slug should get some consideration as it sets the arc on the jaw gripping faces and as such, will effect the arc gripping the parts you are cutting.  For a universally used chuck, normal suggestion would be to use the largest diameter that the chuck is designed to grip so that the jaw's arc is appropriate and never gripping on the corners of the individual jaw's arc, especially with soft (non-hardened) jaws. 

That's the normal but can also introduce some error when the jaws are used on a much smaller diameter part due to minor errors in the scroll and the additional scroll teeth engaged due to the different position of the jaws in the chuck at that smaller diameter.  This is normal to some extent but should easily stay within .001" or better.  It will be better or worse depending on the quality of those parts as well as use or abuse. 

The most common use for soft jaws is to machine a set for a particular job, including irregular shapes.  When utilizing them that way the jaws should be bored with a stabilizing slug that's the same diameter of the part, affording the very best grip and most accuracy.  Also, instead of removing the step left deep in the jaw, that can be left and utilized as a stop for reliable depth setting for repeat parts.  With the basics covered your imagination can start to see all sorts of rigs that can be made for a particular job.
 
And don't forget the four jaw!  Can be quite useful!
http://www.taigtools.com/c1030.html
[/quote]

[narrowminded]

Ummmm... yeah... what he said.   

Seriously, narrowminded, what you describe about making your own cutting tools is pretty much what I do.
I have some of those HSS tool "blanks" you can get online, on eBay, at Micromark, almost anywhere.  They
are pretty cheap if you find a good deal.  I use a Dremel with a Difco cutting disk (it's thinner and smoother than
the rough-hewn Dremel variety).  That let's me cut away from the edge I'm trying to make, so I can fade the
steel away from the cutting edge on all sides (just like you recommended!)

Occasionally, I dress off the edge again with the disk when it starts to lose its sharpness.

The truth is (and take that with a grain of salt, since I'm such a machining newbie)... the machining we are going
for these models is pretty crude compared to what a real machinist with top-grade mills and machines can do.
Those folks talk about "tenths"... LOL!   Nothing I ever do will be down in the 10-thousandths-of-an-inch world
for accuracy.  If I get things to within a few thousandths, I'm thrilled.

I hope that wasn't taken as a slight to what you're doing as that's totally NOT the case.  And if you weren't already doing that, like having a cutter not relieved sufficiently, you wouldn't have successfully made the parts you did.  My answers, in general, are made to possibly add to the immediate conversation and/ or to embellish for those who are watching with interest but may not have tried something like this or have tried and had difficulty.  It's to hopefully help or even encourage them to do so with some advice to get them at least aimed in the right direction.  And because this is an area that I can help in, I try.  NOW, the day will come and even has where I'll be needing some help in my less expert areas, like just about ANYTHING to do with prototypes and many of the resin and white metal casting techniques/ tricks I've seen.   Then there's scenery techniques... and so on.  I get a lot from many of these threads, even ones I've got a fair handle on.

[Chris333]

I was just thinking of the example here, .039" tubing. There is no way I could hold that without a drill chuck. I have a standard set of collets:
http://www.taigtools.com/c1040.html

I could use the 1/8" collet and 1/8" rod and turn it down to .039", but that is not what we are trying here. I just want to be able to mount a drill chuck for small stuff.


As for truing the soft jaws. The problem is you have to clamp down on something like you said. If not the jaws will move just from turning on the lathe. And if I have to clamp something to bore then I can only bore till I hit that. So I can only use the jaws as deep as I just bored them. Either way I'm not gonna get .039" tubing in the 3-jaw chuck.

[robert3985]

So I was just playing with the lathe. How do I mount a regular chuck in place of the 3-jaw chuck? Do I need a whole new tapered head stock that can use a draw screw?

This is what I have now:
http://www.taigtools.com/c1050.html

OK it looks like I need this:
http://www.taigtools.com/c1140.html

I put new "soft" jaws on my 3-jaw chuck and for some reason I can't get them centered.

What @narrowminded said.

I can't give you much advice on your lathe setup because I'm working with a different animal....

Photo (1) - Here's my lathe's 3-jaw chuck & cutoff tool holder:


Bought this from Sears while I was in the Navy at Whidbey Island NAS...a 6" Craftsman Lathe made for Craftsman by Atlas. The year was 1976, and I was deep into scratchbuilding American sailing ship models professionally.  Can't tell you how many brass belaying pins I made on it.  It's been a great setup for model railroading too and is the exact model of lathe I learned how to machine on when employed by a startup company named NORTEC when I was 15 in Richland WA.  I updated it 15 years ago with a quick-change tool post, which was a great upgrade.  Even 40 years ago, this lathe with the accessories, tooling, motor and bench cost me right at $1,400.  The price of machine tools has actually decreased since then due to the invention of CAD and CNC manufacturing.

The only advice I'll give @Chris333  is to get a chuck for your lathe that's got hard jaws...a four-jaw, self-centering one for small stuff would be ideal IMO...

Cheerio!
Bob Gilmore

[mmagliaro]

I hope that wasn't taken as a slight to what you're doing as that's totally NOT the case.  And if you weren't already doing that, like having a cutter not relieved sufficiently, you wouldn't have successfully made the parts you did.  My answers, in general, are made to possibly add to the immediate conversation and/ or to embellish for those who are watching with interest but may not have tried something like this or have tried and had difficulty.  It's to hopefully help or even encourage them to do so with some advice to get them at least aimed in the right direction.  And because this is an area that I can help in, I try.  NOW, the day will come and even has where I'll be needing some help in my less expert areas, like just about ANYTHING to do with prototypes and many of the resin and white metal casting techniques/ tricks I've seen.   Then there's scenery techniques... and so on.  I get a lot from many of these threads, even ones I've got a fair handle on.

Not at all, man!  Your post was very helpful and full of good info.  My response was just meant to say, "yeah.. I agree with you about making your own cutters".

As for machining this small stuff, as you can all see, I often use a simple 3-jaw drill chuck in my mill.  It works shockingly well.  You many recall that I put a dial indicator on a piece of round stock chucked in that thing and it was good to within, if I recall correctly, .001".  It's actually better than the same piece of stock held in a collet in my collet chuck. 

I use the collet chuck when I do things like cut traction tire grooves, because the collet has 6 "jaws" and so it puts more uniform, distributed pressure on the wheel (so it doesn't mar the wheel, or crush it out of round).  But mostly, I use that
drill chuck.

And what narrowminded said to the effect of, "Don't EVER try to mill heavy stock in a drill chuck"   MAN, YOU KNOW IT.
Remember, a drill chuck is not designed to take sideways pressures to begin with.  It can also vibate open and let your stock go flying into your face.  Imagine a piece of steel spinning at 1000 rpm deciding to suddenly pull out of the chuck and go flying in whatever direction it bloody well pleases.  DUCK!
Or worse... imagine the whole chuck vibrating out of its holding arbor and flying at your head.
No... it's okay for tiny miniature pieces with very low cutting forces.  But not for anything else.

[narrowminded]

As for truing the soft jaws. The problem is you have to clamp down on something like you said. If not the jaws will move just from turning on the lathe. And if I have to clamp something to bore then I can only bore till I hit that. So I can only use the jaws as deep as I just bored them. Either way I'm not gonna get .039" tubing in the 3-jaw chuck.

The last sentence in this paragraph addresses that.  You have to cut that step out for a universal chuck.  It could be left as a stop if it was for a specific job.

To true soft jaws you place a round, shallow/ thin piece of material deep in the jaws and clamp on it, sufficient to stabilize the jaws, leaving the bulk of the jaws' gripping face exposed/ hanging out.  It is that overhanging part of the jaw that you then bore just until you are cutting on all jaws.  They are now trued to the machine.  If the jaws have steps for various diameters and the chuck is to be used universally, not for a specific job, you would repeat this step for each step until all are trued.  If they have "outside" steps for gripping internally, those steps should also be cut externally so that all gripping faces are trued.  The various steps may all be cut at the same time with the same stabilizing slug in place but often swing constraints will prevent that.  In that event, finish the sets you can access and then use an appropriate size slug for the steps left. That's it.  If the jaws aren't already numbered, now would be a good time to do that.  As you wind them out and get near the end of travel, start to move a little and then tug on the jaws so that you find the first to disengage from the chuck scroll.  That one will be #3.  A little more, then that one will be #2, and finally #1.  Then they assemble as #1 first, etc.  With the jaws now removed, by hand or in the mill, cut away the small slug left where the stabilizing slug was, preventing cutting at that point. 

If you want to grip an odd size in your collets, with your lathe you can make a sleeve with an OD of one of your collet sizes and an ID of the irregular increment you need by drilling with your number/ letter drill set.  Might even be a time to use the small end mill as a boring bar trick if the hole is big enough and you have a tiny enough end mill (I've used .015" end mills like this for .02something" bores).  Turn the OD and drill the ID in one setup in your lathe to assure concentricity, cut it off, saw split it with your track saw or a narrow jewelers saw so it can collapse like a collet, and you've got your reducing sleeve.  This works because the sleeve acts like a collet within a collet and it remains centered because the sleeve has a uniform wall thickness so collapses the minor amount it has to to grip, still on center, for that reason, the uniform wall.  This I've used often especially to grip odd tap shank diameters for power tapping.

While we're at it, I have made a crude collet like this with a very beefy wall relative to the hole, and used to grip a square bar in a three jaw chuck.  In that case you are depending on a fairly rigid wall on the sleeve so that it doesn't distort too badly in the spans but it will close pretty darn solid and surprisingly well centered on the four corners while being closed by the three jaw chuck.  Center the split in one of the jaws, insert the square bar spanning that split with two of the corners of the square, and tighten.  This is handy if you don't have a four jaw or are willing to accept a couple of thousandths off center (IF it even does that) and don't want to screw with the four jaw and indicator.  It's also quite fine if you're just trying to face the bar to length.  "Heavy wall" might be something like 3/8" OD or bigger for a 1/8" square bar.

Remember the number .7071 for machining or just designing.  Round diameter X .7071 = the square size that will fit in that circle.  Square size divided by .7071 = the corners of the square (diameter). That would be the way to know what the bore needs to be in your square bar gripping collet.  For hexes the conversion number is .866.  Not needed for three jaws but still a handy number around the shop. The 7071 number can also be used to easily work out 90 degree lever and link travels.  Half the diameter is the lever length and the square is the 90 degree travel.  Think about it and you'll see it.   And all for just remembering .7071. Or .866 for hexes.

And as I think more about it, a very close fitting sleeve with a good ID finish (reamed?) might support pretty thin walled tubing without an arbor.  Cutting gently right up against the sleeve, minimal projection, might get it done as it's all compression and uniform.  Don't overtighten but it won't take much.  Can't promise that but if I had a bunch to do, I'd try it and wouldn't be surprised if it worked.  A true running spindle might be a key to it, too.  Now I'm on an excursion.