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Plans, projects and how-to's for home machinists

Grinding Lathe Tools on a Belt Sander – For the New Guy

I’m a believer.  As a new guy I totally sucked at grinding lathe tools.  It’s almost painful to admit how many stubby, misshapen, multi-faceted, overheated and just plain ugly lathe tools I made back then.  The amazing thing is that some of those tools actually worked as well as the pre-ground tools that came with my lathe.  I started to believe those guys that tell you, “… just get it close and it will work.”  Of course, I was too embarrassed to call myself a hobby machinist with those Franken-tools so I bought an expensive set of inserted tip carbide tools that I thought would make a major difference but was disappointed.  They couldn’t rough as deep or finish as well as my ugly high speed steel (HSS) tools, at least not on my lathe, so then I believed those guys that tell you, “… stick with HSS on a hobby lathe.”  Hey, desperation can make you mighty receptive, you know.

Fast forward 15 years and now I believe, after having ground many experimental tools, that the best lathe tool for a hobby-class lathe is a HSS tool with its tip geometry modified to reduce the cutting forces it produces, ground on a belt sander.

Since standard tools are intended for use on industrial lathes their geometry can produce cutting forces that are excessive at times, especially when roughing but this can also affect sizing and finishing cuts.   To be clear, cutting force is that force produced by the tip geometry of the tool that must be overcome to make a cut.   We can look at it as a continuous resistance generated by the shape of the tool as it is pushed through the material during the cut.  A standard HSS tool has a broad, wedge shape and creates a lot of resistance (carbide is even worse), so we must dial down our control inputs (depths of cut, feeds and speeds) to use them.  If we alter the tool so it has a narrower included angle it cuts with less resistance, thus lowering the rigidity and power needed to make a given cut.We still have to manage our control inputs but since the cutting forces are lower we would expect to be able to cut deeper, achieve better accuracy in sizing and finishing cuts, and finish better with greater ease before running into the rigidity and power limits of the lathe. And this is exactly what happens.

To demonstrate this I took a 0.050” deep cut in 12L14 mild steel on my admittedly older hobby-class manual mini-lathe using a very good quality inserted tip carbide roughing tool with a new insert, a sharp freshly ground high speed steel (HSS) roughing tool with standard tip geometry ground for steel, and the general purpose tool with modified tip geometry (not optimized for steel) that was ground for this discussion.

The carbide tool made the cut but chatter was excessive.  Speed was as low as I could reasonably go and the feeding force was very high.  The finish is really ugly due to all the chatter and the chips are tiny and powdery.  Reducing the depth of cut to 0.010, the proper depth of cut for this insert, allowed it to cut as it should.
The HSS roughing tool did fair but there was a lot of chatter.  Speeds and feeds had to be adjusted almost constantly to make it this far.  Finish is rough but not excessive for a roughing cut.  Chips are tightly curled due to the standard side rake.  Reducing the cut to 0.030” allowed the tool to work much better.
The modified tool cut easily, speed was about 100 RPM higher than with the other tools and there was no chatter at all.  Finish is much better compared to the other tools.  The chips look more like loose shavings due to the sharper included angle at the tip.
Chips from the carbide tool, HSS rouging tool and the modified tool are distinctly different.  You absolutely cannot fake a chip.  They tell you exactly what is going on at the tip of the tool.

Continue reading Grinding Lathe Tools on a Belt Sander – For the New Guy

Modifying a Craftsman 2 X 42-inch Belt Sander For Tool Grinding

The Craftsman 2 X 42-inch belt sander is a very good general purpose belt sander.  With its 1/2 HP motor it can handle most light duty work in the shop, including grinding lathe tools for both metal and wood lathes.  This grinder allows for very fast belt changes, tracks well with a simple adjustment and has enough power to grind tools without overheating or bogging down.  However, it does have two deficiencies that must be addressed before any serious grinding can be done on it — the main grinding table and the platen.

The OEM table is made of cast aluminum.  It pivots on and locks with a single large screw.  Firm pressure on the table can overcome this screw and the table will move with the belt running, which is very dangerous.  My advice is to dump it and build a decent table.

The OEM platen is stamped mild steel.  It is okay for light use like shaping Popsicle sticks but will not last long grinding lathe tools.  The platen is mounted solidly to the chassis and is fairly stiff but pressure on the belt will wear a divot into it quickly so basically it’s useless once this happens.

Resolving these deficiencies isn’t difficult but it requires some fabrication.  I’ll show you how I addressed them.

The Platen Fix

A grinder platen has to be solid and unyielding, flat and ideally long wearing despite driving a grinding belt and grit over its surface.  No steel platen I know of will withstand this kind of abuse for long but a ceramic glass liner will.  This liner is actually a high temperature glass material originally developed by Corning and is commonly sold by knife making suppliers in 2-inch wide X 1/4-inch thick slabs of varying lengths.  Commonly known as Pyroceram, it is usually mounted to a steel backing plate with JB Weld.  This stuff is highly wear and heat resistant and only a full-time knife maker is likely to ever wear one out.  If you do no other mods to your grinder at least do this one.

I used a 2-inch wide X 9-inch long X 1/4-inch thick piece of O-1 precision ground steel as a platen/backing plate because I wanted a flat mounting surface that would not move with heat over time.  I know that mild steel can move with localized heat and while this may not break the epoxy bond … it might.  So far, I have had no separation issues so this worked for me.

I drilled and tapped two 1/4-20 holes on each edge so the platen can be flipped over if the liner ever wears on one end.  A piece of 1/8-inch thick X 1.5-inch wide angle iron (not aluminum) is used to attach this backing piece to the side of the chassis using the OEM screws and platen mounting holes.  The mounting holes in the angle iron are slotted to allow squaring of the platen to the belt.  Offset your platen and chassis screws if you copy this; the way I did it works but it would be better if the screws were clear of each other.

Before attaching the liner to the platen, be sure to lightly bevel or round the side edges of the liner and more generously round the top and bottom edges to prevent cutting the belt.  This is best done on a slack 50-60 grit belt.  The sparks will be orange and the glass will glow but it grinds easily enough.  I also lightly sanded the side of the glass that would bed in epoxy using sandpaper overlying some plate glass to give the glass some tooth.

I put some oil on the tip of some 1/4-inch screws and use nuts to lock them down with their ends just flush with the epoxy side of the steel platen.  This is to keep the holes clear of epoxy.  After cleaning both contact surfaces with lacquer thinner, a 2 X 9 X 1/4-inch piece of Pyroceram is bedded onto the face of the platen with an even layer of JB Weld.  I covered the face of the glass with a thin piece of plywood and clamped it with 4 spring clamps and allowed it to dry for a full 24 hours.  JB Weld has the highest heat tolerance of any commonly available epoxy, at least to my knowledge.  Ideally, you want to have a ledge under the glass liner to keep it from being knocked loose but mine has been stable for many years without a ledge.  Be sure to use blue Loc-Tite to attach the platen to the grinder chassis so it won’t vibrate loose but can be easily removed if needed.

In use, the Pyroceram platen is used like any other platen.  Since it is glass you should avoid slamming hard objects into it but otherwise it is tougher than nails.  I have ground hardened steels, tools, and other assorted materials and have yet to see any indication of wear or movement over the years, though the picture shows some transfer of paint from the back of the belt.  Pyroceram is some truly amazing stuff.  The piece I used cost $20.00, delivered!

The Table Fix Continue reading Modifying a Craftsman 2 X 42-inch Belt Sander For Tool Grinding

HSS Indexable Inserts

It’s not obvious at first but this video is about the Arthur R. Warner Company’s HSS indexable inserts.  After seeing it I’ve decided that I would really like to give them a try.  I know you can get a better finish with HSS bits but I don’t like having to stop to sharpen them.  So I use carbide inserts.  I get a pretty good finish with them and I can cut with a tip for hours before it wears out and I have to rotate the insert to a new one.

It looks like the Warner Company’s inserts give you the advantages of HSS along with quick and easy sharpening.  When a tip on the insert gets dull you can rotate to a new one in seconds without losing your lathe bit’s position.  And when all 3 tips become dull you can sharpen them by rubbing the top surface of the insert on a whetstone for a few seconds (see video at 2:30).

Unfortunately, they don’t seem to sell inserts that will fit my tool holders (TCMT32.52 for my 8×12 and TCMT 21.51 for my 7×12).  So if I want to give HSS inserts a try I’ll have to buy a 5 bar turning kit for about $128 or somehow find the time to make a bar that will fit their inserts.  The price of their kit is considerably more than what I paid for my imported insert holders but it seems reasonable for a quality American made product.  Has anyone bought one or tried their inserts?

How I tram my mini-mill

This is how I tram my mini-mill.  I think the method I use is fairly common, although I may use slightly different equipment than others.  There are other ways of doing it and some people have strong opinions about which way is best.  I’ve included links at the bottom to some interesting discussions I found if you would like to learn more.  If you don’t know, tramming is the process of adjusting the mill’s column so the spindle is perpendicular to the table.

By the way, this procedure only trams the X-axis.  Unlike most other mills, the mini-mill’s Y-axis is not adjustable, although there are ways of doing it if you’re willing to go to the trouble.

My Equipment

  • A matched pair of 1-2-3 blocks
  • A digital dial indicator
  • The fine-adjustment arm from an inexpensive magnetic base for a dial indicator held in a 5/8-inch cross-drilled piece of drill rod mounted in a collet

I started using the arm from a magnetic base because it was the quickest and easiest way to mount a dial indicator so I could read it from the sides of the mill.  It replaced a home-made one that had the DI facing forward (good) and to rear (hard to read).

If your mill vise is big enough you can measure on the top of it with a dial test indicator (DTI) and tram your mill that way.  The vise shown in the picture is probably big enough to do that.  But the screwless precision vise I often use isn’t, which is why I use the 1-2-3 blocks, a trick I learned from someone else.  The blocks will also allow you to tram your mill without removing the vise.  I also believe you can get better results by taking your measurements farther apart.

For Best Results

Before you get started you should swing your indicator from one side to the other a few times to make certain you get repeatable measurements and there is no “play” in your setup.  You should also center your table under the spindle and make your measurements on its center line and at the same spots each time.

You should know that tramming your mill’s table does not guarantee your vise will hold your work pieces square with the spindle.  It should if it was made properly.  If it doesn’t you should find a way to fix it, consider getting another one or tram your vise instead of the table.  I’m talking about your vise being square with spindle, not with the table.  That’s also important, but it’s different topic.

One way to check your vise is to tram your table, mount a long parallel in it, and then measure at the ends of the parallel with your indicator.  It should be just as perpendicular to the spindle as your table, or pretty darn close.

It’s Easier with a Digital Dial Indicator

In the past I’ve always trammed my mill using a traditional dial indicator with a needle and dial.  Sometimes it would take me just 2 or 3 minutes but other times I’d be scratching my head for 10 or 15 minutes and wondering what the heck I was doing wrong.  It was usually because I’d gotten confused reading my “analog” indicator, which is easy is for me because as an amateur machinist I don’t use one very often.  So the last time that happened I took my old indicator off and replaced it with the new digital dial indicator I’d bought from Harbor Freight for about $25 (with a 20% off coupon).  It instantly put an end to my confusion.

The Procedure

The procedure is simple with a digital indicator.  Swing your indicator to one side and zero it.  Then swing it to the other side.  If the measurement is “negative” then push the column toward that side half the distance shown on the indicator.  If your measurement  is “positive” then push the column away from that side half the distance shown.  Then zero the indicator again and swing it to the other side to check your work.  You want to try to get the same distance on each side,  although I wouldn’t worry too much if you’re only off a thousandth or so over a good distance (my setup takes measurements about 10-inches apart).

If your indicator has a needle, then use it to find out which side has the shortest distance between the indicator and the table, and then “zero” it or write down the measurement.  Then swing it to the other side, calculate the difference in length and push the column toward that side half that distance.

Before you can adjust the column you’ll obviously have to loosen the big nut on the back of it a little.  There’s a good chance that the column will move slightly when you tighten it again, so re-check the tram.  I’ve found you can minimize that if you loosen the nut just enough to allow you to move the column by gently tapping it with a rubber mallet.

More information

CraftKB: How to tram a Sieg X2 mini mill

Practical Machinist Forum: How to tram a mill for best surface finish / flatness?

Random Quote

The confidence of ignorance remains unimpaired, and we have to suffer for it.

— Mert Baker