Making Chips

Swarf - Chips and Curls

Making the first chips with the stock 4-way tool holder and some HFT carbide tools was not nearly as fun as expected.  I picked up a set of 5 carbide tipped 5/16" tools.  It included: standard turning, left, right, straight and cut-off tools.  They weren't pretty and gobbed with paint, but looked like they would do ok.  The main reason I got these was the 5/16" size which works out pretty close to center-line on the chuck and stock in the 4-way tool holder; it wasn't necessary to shim the tool every time.  They did work ok on brass and aluminum but steel, even mild steel, was not pretty. 

For steel, I tried a myriad of things with speed and feeds and moving the tool as close to the post and centered over the cross slide as best I could, but ultimately (I think) the radius and relief of the tool were too large and too shallow.  No matter how shallow of a cut, it still chattered and left marks that had to be removed with a file and emery cloth.

I made a few things the first month with these tools while getting to know this machine.  After a few weeks though, I found an old 5/16" HSS/cobalt bit in the back of one of my boxes.  It worked great on brass after I touched it up a bit on the grinder and it actually worked pretty well on mild steel.  The first useful thing that came out pretty well was a center tool made from a piece of 3/8 steel.  The second was a brass bushing for my Test indicator to fit in the magnetic base holder.

After that first month I had saved enough shekels to buy the Little Machine Shop's Tooling Package for the Mini Lathe.  It included an arbor and 1/2" Chuck for the tail stock, a set of center drills, a set of 3/8" indexable cutting tools, a 3/8" boring bar set, a P1N cut off blade, and most importantly a Quick Change Tool Post with holders for everything.  It's been worth every penny, making pretty short work of any job on the Mini.  I highly recommend it!  Note: the tail stock arbor on the Mini is a Modified (Short 2MT, no tail)...a standard 2MT won't fit.  Little Machine Shop has several styles that work on the mini for great prices.

The cutting tools came with carbide tips with a 1/64" radius.  They have worked well with most material I have tried, however the tiny radius will leave a little groove at the standard feed rate on steel on the Mini.   However if I only take about 1-2 thousandths on the final pass I can touch up with medium to fine emery and have a pretty finish.

On aluminum and brass I can make curls 2 feet long with these tools sometimes, but have to be careful not to let it get it caught in the works.  There are several schools of thought on chip shapes.  Back in the 80's at a machine tool technologies course, I was taught to make longer chips but to keep an eye on them and break them off if they start getting caught in the works.  Out on the web you will find people talking about the benefits of small curls, and they may be right I just haven't played with tool geometry enough to know better...other than I get a pretty good finish with the longer ones and don't have to take a final tiny cut to get a decent finish, particularly on soft metals.

The most difficult material I have cut on the Mini was a piece of 2" G2 Grey bar.  I used it for its density mainly (and it's what I had laying around) but it was sloooow going and made more of a powder than chips or curls, basically using the slowest speed and feed I could get and taking tiny cuts of about .004 or less.  Luckily it wasn't necessary to take much off other than to true it up and get as good as I could with tools then move to a fine file, then course, medium, and fine emery and finally some fine crocus cloth at the end to get the desired finish.

Delrin is a breeze on the Mini and the good tools don't allow a lot of spring back unless you take too deep of a cut.  However the curls are a pain as they want to walk up on the part sometimes and seem to weld themselves a bit making little lumpies sometimes.  If you stop the lathe at the end of a feed you can usually peel them back with a fingernail or a pick.  Brushing won't break them like some softer metals.  Also, by changing your attack angle a skosh they will peel the other way most of the time.

Parting on the Mini is always interesting.  I have gotten pretty good with the P1N blade on smaller diameters, but larger diameter stock gets a bit tricky.  The P1N is a .040 x 1/2" blade, so heat and depth become an issue.  On larger diameter stocks I found it good practice to cut a .1" notch with a standard tool then put the cut off on and walk in a bit, then back out and move over, close to a blade width at a time.  Going back and forth and in and out over that .1" notch allows the chips to fall out well and doesn't overheat nor tend to hog in if I feed too fast.  Actually the blade will flex a bit on a larger piece using this technique.  I finally picked up a P1 blade which is 1/16 x 1/2" and found it a little better for larger stock but still use the back and forth technique with good results and a clean part. 

Another important tip is to only have enough of the blade sticking out to part the radius of the stock you are parting.  Also make sure your blade is in the holder Perpendicular to the work.  The P1N blade has a little raised section in the cutting zone and will cant in the holder if you just slap it in and tighten it.  If you have a counter bore through your part...only go that deep...and set the blade depth accordingly.
  This also helps with hogging in and blade flex.

I did a lot of research on the web about parting on these little machines and found the following link has some real good tips on grinding and feed rates, etc.  This is one of my favorite sites; he is associated with a Connecticut group of Mini-users.  It is packed full of tips, tweaks, great mods, and procedures that really helped me get my feet on the ground.  If you are a relative newbie it is a great starting point to learn a great deal quickly.

GadgetBuilders' groove idea (on the top of the parting blade) does significantly well at dispersing the chips.  The trick is getting a groove less than a 1/16" wide.  I did it with a Dremel also, and found a tiny circular stone that allowed me to do a decent job after a couple of tries.  The gibs have to be adjusted for minimal slop in the slides.  Not so the handles don't turn well but enough to minimize any play in any of the gibbed components.  The initial cleaning and polishing of the gibs seemed to help get me through my first partings. 

Another trick that works well when parting is to make sure the top of the tool is about .o10-.030" above center line.  The tool will still give you a good part across center because the 7° rake on the front will still cut the center tip off.  Also GadgetBuilders' tip of grinding a slight angle to the face works great, leaving a very clean face to the part you drop off.

One thing to be aware of on the Mini is it is pretty much a constant vigil to keep the gibs running smooth and tight.  I usually adjust them after 2-3 jobs; even sooner after working with steels.  The more you do it the faster you get at it although it is a bit tedious to get it right.  You will however be rewarded with less backlash, nice smooth cuts, even chips and decent parting without hogging in!

Subpages (1): Knurling