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

[robert3985]

Y'know....it's times like these I'm very happy I've got a lathe and mill....All I do with my SS hypodermic tubing is chuck it up, face it off...run the tool post slide towards the chuck adding in the thickness of my cut-off tool, and part the short length of tubing off.

I can repeat this operation as many times as I want, and get exact results every time...all with about five minutes of setup time for the first cut.  It is one of the most simple of machining operations to be done on a lathe.

One of these days Max, you really (I mean REALLY) need to spring for a lathe and mill...and instead of taking days to figure out how to do something as simple as this, you can do it in a few minutes.

Cheerio!
Bob Gilmore

[Burlington Bob]

If it was easy, everyone would do it!

[peteski]

Y'know....it's times like these I'm very happy I've got a lathe and mill....All I do with my SS hypodermic tubing is chuck it up, face it off...run the tool post slide towards the chuck adding in the thickness of my cut-off tool, and part the short length of tubing off.

I can repeat this operation as many times as I want, and get exact results every time...all with about five minutes of setup time for the first cut.  It is one of the most simple of machining operations to be done on a lathe.

One of these days Max, you really (I mean REALLY) need to spring for a lathe and mill...and instead of taking days to figure out how to do something as simple as this, you can do it in a few minutes.

Cheerio!
Bob Gilmore

Bob,  how wide is your cutoff tool blade?

The one I use on my Sherline is 0.040" wide and I can't imagine using it to cut off a piece of thin-wall 0.039" OD hypodermic SS tubing. 

PS. Max does have a mill which he uses as a lathe too. 

[robert3985]

Bob,  how wide is your cutoff tool blade?

The one I use on my Sherline is 0.040" wide and I can't imagine using it to cut off a piece of thin-wall 0.039" OD hypodermic SS tubing. 

PS. Max does have a mill which he uses as a lathe too. 

Peter,  For really small stuff, I custom grind my cutoff tools.  The one I am using now has a tip width of .020" with a taper towards the tailstock so the part falls off cleanly cut, and then I proceed to cut a bit further and it faces off what's chucked up, doing two operations in the same cut.

I don't cut off pieces as small in length as what Max wants to do, since I use my tubing for signal masts.  However, if I were to cut off short length pieces, I would run my tailstock up close with a smaller piece of brass or steel rod sticking into the tubing so when the part falls off, it's captured by the rod in my tailstock chuck.

I run my lathe up to maximum speed also and use Tap Magic Pro Tap as a cutting lubricant on SS.  Works great for me!

Cheerio!
Bob Gilmore

[peteski]

Thanks Bob!  I'm not very experienced with grinding my own tools. Do you start with a standard cutoff blade or do you just use a regular square 1/8" or 1/4" HSS or Cobalt blank?

[Chris333]

Plus how do you chuck up 0.039" tubing without a $600 set of WW collets? And Max is using a mill as a lathe so even less chance he can use WW tapered collets if he had them.

[rrjim1]

Plus how do you chuck up 0.039" tubing without a $600 set of WW collets? And Max is using a mill as a lathe so even less chance he can use WW tapered collets if he had them.

The three jaw chuck that is included with a sherline lathe can chuck up a lot smaller stock than .039. The chuck will also fit on a mill.   

[robert3985]

Thanks Bob!  I'm not very experienced with grinding my own tools. Do you start with a standard cutoff blade or do you just use a regular square 1/8" or 1/4" HSS or Cobalt blank?

Peter, I use 1/8" HSS blanks most of the time, but I have ground standard cutoff blades too.  Both work well, and there's a lot less grinding to do on the standard cutoff blades.

Plus how do you chuck up 0.039" tubing without a $600 set of WW collets? And Max is using a mill as a lathe so even less chance he can use WW tapered collets if he had them.

@Chriss333 ,  The SS hypodermic tubing I use is .036" OD and chucks up just fine in my 6" Atlas/Craftsman lathe's 3-jaw chuck.  I do have collets, but they sure didn't cost me 600 bucks!

I have a Sherline mill too, and it would be easy to chuck Max's .039" OD tubing into the milling head using the Sherline drill chuck.  Cutting it off at a consistent length would be something I'd have to think about using the mill. 

Okay, now that I've thought about it...here are a couple of photos to illustrate maybe how it can be cone with the mill....





Ya gotta custom grind the cutoff tool.  I use 1/8" HSS stock and don't make it very long.  Also make the tubing protrude as little as possible out of the chuck and turn up your speed to maximum.  Get an exact measurement of the width of the cutoff tool (should be in the neighborhood of .020"), then run your mill down so you just kiss the edge of the tubing...and face it off slowly and smoothly using your X-Y table.  The cutoff tool should be exactly centered on the diameter of the tubing when looking directly downward so that the top cutting surface of the tool at the tip is exactly centered.   

After you make the face-off cut, move your mill doward the length of the part you want to cut PLUS the width of the cutoff tool, then carefully cut it off slowly and smoothly using a bit of oil as a lubricant.  Insert a .020" wire into the tube to catch the part you cut off.

The trick will be to get the cutoff tool ground precisely.  I use a combination of my bench grinder...making sure the HSS steel never turns blue by dipping it in the water containter often.  This takes off the most metal...then I use Dremel cutoff disks to complete the tool, working slowly and carefully...once again dipping the tool into cooling water so it never changes color.  You should make sure that your grinder wheels are properly dressed with sharp, square edges before starting to remove metal.

I didn't triy this setup as it's now 5:38AM...and I'm gonna hit the hay to get a few hours of sleep....

But, I hope this will work for you Max...

Cheerio!
Bob Gilmore

[mmagliaro]

Folks:

1. I can chuck .039" (and  lot smaller), in my 3-jaw chuck in my mill.   
2. I have made my own cutting tools (as you've seen, like the ones I made to cut domes and my driver tires).  I make them out of either 1/8" or 1/4" HSS tool blanks, usually,  They can be cut and shaped by hand with a Dremel with a diamond cutoff wheel and diamond files.  I also have a length of O2 steel bar that is  1/16" thick x about 3/4" wide.  I have made tools out of piece of that as well.  O2 is darned hard stuff, though.  Very hard to shape and I never feel like I get quite as sharp a cutter edge on it as I do starting with HSS blanks.

Parting off small pieces of tubing... like so


But...
I didn't think that any of these cutters would do a good job parting off piece of stainless steel.  Stainless is so much harder that I figured the cutter would just grind and grind against it and either bend or smash the tubing, or just go nowhere.  That's why I didn't go down that road in the first place.

I'll give it a go.

[Lemosteam]

Max, I was going to suggest exactly this, except I would put the shank diameter behind the cutter instead of the flutes (in case you over-run the cutter it won't get caught in them).  This allows the part to fall straight off into box after cutting and provides backing for whr the cutter breaks through the tubing.

[mmagliaro]

Max, I was going to suggest exactly this, except I would put the shank diameter behind the cutter instead of the flutes (in case you over-run the cutter it won't get caught in them).  This allows the part to fall straight off into box after cutting and provides backing for whr the cutter breaks through the tubing.

Yeah, that photo isn't a good textbook example of how to do it.  You are right.  The flutes should not be behind the cutter.
At the very least, they will damage the cutter when it breaks through.  I think that photo was "staged" to be honest.
I cut it, and then I wanted to set it up to take a photo so I just slipped everything together like that and took the picture.

[Chris333]

  

Guess I never thought of using a chuck in that side of a lathe, even though I use it in my mill...

I think there are like 50 collets in a WW set and if bought separtly they are about $20 a piece. Here is an old set:
http://www.ebay.com/itm/49-Old-Odd-10mm-Watch-Collets-Elgin-Watch-Factory-Watchmaker-WW-/391433521098?hash=item5b234187ca:g:wgQAAOSwv9hW51Tp

Long ago I used hypo tubing to make Z scale crossbucks and I slid it over an old bit in a pin vise and sliced them with the Dedeco blades.

[narrowminded]

Parting off small pieces of tubing... like so

Whether in a lathe or a mill, this is the way to do it.  Make sure your tool has back relief from the cutting edge and the tool is on C/L.  Sometimes it's easier to grind the back relief on one edge only and then clamp the tool slightly tipped for the opposite relief. If your arbor extends through the part an arbor material that is machinable will help save the cutting edge. If you can position the arbor up inside the tubing just above the cut position it will still afford the support for clamping while avoiding your tool hitting the arbor.  And best, if you can control your arbor position, have a relief in it right at the tool position.  That's not always practical depending on the quantity of the parts but sometimes positioning the tube without the arbor, gripped lightly in the chuck so as not to crush it, and then inserting the arbor to depth with a small removable probe while final tightening, can be rigged to work.  The basic concept is there and some imagination bouncing around that basic idea will present alternatives for your actual task.

And for Chris and all, if you're looking for high speed tool steel, don't hesitate to grind up the shank of an old HSS drill bit.  Flatted to C\L just at the end where you're making the cutter edge, ground at the angles you want, and you're set to go.  Especially if you're just making a light cut, you can grip just that in your vise and if you support the jaws at each end with pieces of the same size drill shank it assists the vise to clamp squarely.  Another assist when clamping round parts in a vise is to insert scraps of aluminum in the jaw faces to help assure a stable grip.  The aluminum will distort ever so slightly around the part, conforming to its shape, which assists the vise in applying a broader and more uniform load on the part (or tool) and dramatically assisting the grip on it.  And if you want to get fancier yet, fashion a tool holder for your drill blank by drilling a hole the size of the shank you're using  in a scrap of square steel, aluminum, brass, or any other scrap you have (and ream it if you have the reamer).  That can be saw slit lengthwise most of the way through the holder, centered on the hole but leaving it joined at the end, and then on the clamping face, undercut with something as simple as a file so that the raised portion left is directly over the bit to be clamped, gripping it much like a collet would grip a part.  OR drill and tap it for a set screw to clamp the shank.  Grind a flat on your tool for the set screw to engage.  I'm partial to collet style gripping for things like this because it allows for infinite positioning options before final tightening, making the setup easier and the grip is quite good. 

If you have no experience grinding cutter edges don't let that scare you.  It's not that hard.  A quick search will get you sites that explain those things well.  They may also be just a little confusing or seem challenging as they'll get all into the various angles and with different angles for different materials which all have some validity but for a quick cut that doesn't need to be optimized for mass production, you'll get it done as long as you have a good edge, at least SOME back relief going away from the cutting edge in all directions (the cutting edge being what's presented to the part to remove metal), and don't get too worried about those angles give or take a degree or two, or five, at least getting started.  Just keep in mind the obvious, that the cutting edge has to be the only thing presented to the material being cut so it's not rubbing on the blank is it's moving past the cut.  And getting too silly with the relief takes away the support for that cutting edge making it prone to breaking.  Also, keep some water around to occasionally chill the cutter as you grind but the likelihood of wrecking the material hardness is slim if you are going easy and in a manner of control that gives you a chance of getting the desired shape.  What's hot to your fingertips is nowhere NEAR the heat required to wreck hardened steel material.  That can also be researched if you care to know.   Good luck!

[peteski]

Thanks narrowminded!

[narrowminded]

Without being directly applicable to this issue but surprisingly little utilized or even considered as an option when working on small parts in a lathe, is is to use a two flute (or more) center cutting end mill as a boring bar.  Really works well especially when trying to bore small holes.  You set the end mill in the standard tool holder (or make a collet type clamp as described above for a drill shank holder) at ever so slight an angle so it's not rubbing on the backside, cutting edge rotated and raised or lowered so as to be square to the cut, drill your pilot hole just as you would do with any boring bar, and let 'er rip!  And each end mill gives you at least two factory ground cutting faces, ready to go.  End mills are available in some pretty small sizes, also in carbide, and often at a fraction of the cost of miniature boring bars.  I've used that not just to get a one off done but even for fairly high quantity part runs where a mini hole needed to have a light bore cut taken.  Because of the nature of the conversation I thought this might be useful to the same folks interested in this topic even though it's not in direct response to the problem at hand.  Hope it's useful some day.