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MachinistBlog.com

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

Pamper Your Tools

I saw this on MadModder.com and thought it was a brilliant idea.  So I asked John Hill, also known as The Artful Bodger, for permission to republish it here.  MadModder is one of my favorite forums and if you visit the discussion about John’s idea you’ll be able to learn more and see a beautiful storage case someone made using it.  — Rob (Chief floor sweeper and editor)

Start with one of these

…and one of these…

Continue reading Pamper Your Tools

Video: Centering a 4-jaw chuck

This is probably the best video I’ve ever seen showing how to center a piece of round stock in a 4-jaw lathe chuck.  I am wondering about one thing though.  Some of the commenters on YouTube refer to centering the chuck the “normal” way.  Well, what is the “normal” way?  This is pretty much the way I do it, although I still haven’t gotten around to making a second chuck key yet.

CNC Fusion Z-axis Modification

This photo shows the modification I made to my CNC Fusion z-axis mounting bracket so I could adjust my top gib screw with a shortened hex wrench

Here’s a modification I made to the Z-axis ball screw mounting bracket on my Sieg X2 (Harbor Freight) mini-mill.  My CNC conversion kit was made by CNC Fusion and their design does not allow you to adjust the top gib screw without removing the column from the base and sliding the head half way off of it, which is necessary to get at a large 10mm bolt that holds it from the inside of the spindle head (along with 2 smaller bolts on the outside).  My post about removing the X2’s intermediate gear has some photographs that will show you how much work it takes.

The bracket actually covers up the top two gib screws and there’s not much you can do about the second one except to adjust it properly before you install the ball screw and then hope you never need to adjust it again.  To make it accessible you’d have to remove metal near where the ball screw nut is attached and I don’t think you can do that.  But there’s nothing to prevent you from making a bigger opening so you can adjust the top gib screw with a shortened 3mm hex wrench.  I also made it big enough so I could get a wrench or at least some needle-nose pliers in there to loosen or tighten the lock nut.  If I’d been able to wait a week or so I would have eliminated the lock nuts altogether by ordering self-locking ones from LittleMachineShop.com.

I have two mills, which made it possible for me to make this modification.   If you don’t have that luxury you might want to consider doing it before you begin converting your mill to CNC.  The original opening was about .60 wide and .38-inches deep.  It’s now .94-inches wide and .55-inches deep.

I’m not sure, but there may also be another solution and that would be to eliminate the internal bolt by replacing it with more external ones.  That would allow you to quickly and easily remove the Z-axis ball screw so you could have full access to all the gib screws.  I think CNC Fusion did it the way they did so their customers would not have to drill and tap any holes in the spindle head.  Their design avoids that by reusing the holes used by the height adjusting wheel and mechanism.  Of course if you used more external bolts you’d have to put them where they wouldn’t interfere with the gears inside the head.  You’d also have to make certain they could handle the weight of the head, which I think is about 12 pounds.  That’s one advantage the big internal bolt has.

I know this is a boring post for most of you.  But I”m hoping it will help others who also have one of these CNC conversions kits.

More Photos Continue reading CNC Fusion Z-axis Modification

Random Quote

Whoever is careless with the truth in small matters cannot be trusted with important matters.

— Albert Einstein