Quick Tips

Last Update: 07-11-2017

This will be a collection of some simple tips and techniques that I have learned from others or by myself over the years and use regularly.

Grinding carbide on the milling machine - 07-11-2017
 Dress resin bound diamond wheels - 07-11-2017
 Grind multi purpose lathe tools - 07-11-2017
 Holding delicate, knurled parts in the three jaw chuck - 07-11-2017
 Quick way to make a radius grooving tool - 27-03-2017
 Grinding external radius lathe tools - 20-03-2017
 Regrinding carbide inserts for special operations - 03-02-2017
 Using a ball bearing to hold rough and non parallel parts in a vice - 03-02-2017
 Centering work on the rotary table - 03-02-2017

Grinding carbide on the milling machine

Robin Renzetti showed at least two examples of grinding carbide on a milling machine using metalic bound diamond tools.
Resharpening a carbide tipped annular cutter
Grinding a custom tool from solid carbide, using the Bridgeport to form the concave radius.

I wanted to try that myself, using very cheap diamond grinding tools, like you would use in a die grinder, in the milling machine. Spindle speed was 2000rpm and I fed the carbide blank (broken endmill..) sideways into the ballshaped diamond tool. It works suprisingly well, the diamond cuts very free, progress is relatively fast.
That way, if you had an additional rotary axis, you could easily grind concave faces for broaches.

With a conical tool, you can grind very nice radius tools for the lathe - Size of the radius is controlled by the depth of the tool in the work and the conical shape creates the clearance angle automaticaly. As it is a round piece of carbide in this case, I ground the other side flat after forming the radius (Just freehand against a diamond wheel) and a simple radius tool was finished.

In my mind this is a great addition to the evergrowing list of small tricks to pull yourself out of a ditch, when you need a custom tool for a rush job.

Dress resin bound diamond wheels

Dressing resin bound diamond wheels is not completely trivial. Robin Renzetti mentioned using molybdenium to dress the wheel and some digging on the internet brought up a patent, explaining exactly that.
Process for truing a diamond wheel utilizing a molybdenum tool - US Patent 3921616 A
I ordered some molybenium roundstock and tried it on my beater-diamond wheel. As you can see by the straight edge, it is anything but flat:

Then I went ahead and used the molybendium instead of the diamond to dress the wheel - Small depth of cut and relatively fast traverse speed less than half a second to get across the wheels face. And slowly, the wheel got back to flat.
After dressing the wheel like that, the diamond grit and the resin binder are at the same level and the wheel does not cut very well. With a sharpening stick for diamond wheels you can trim the resin back and expose the diamond:

After the dressing/sharpening process, I am left with a perfectly flat wheel again:

It is a good idea to use dust extraction, the process creates a lot of molybdenium dust, that you better not breathe.

Grind multi purpose lathe tools

I have often small production runs of 10..50 parts on the lathe and if I can save one or two toolchanges, work goes so much faster - One trick that I do a lot is to grind multi purpose tools, that can do more than one operation.

The first one is a Horn 312 parting insert, ground to do parting, facing and outside turning:

This is a Hss tool, specific ground for 27° chamfers and to face the part:

Holding delicate, knurled parts in the three jaw chuck

I had to machine knurled parts - Basicaly a simple part out of aluminium, straight knurl. Machined directly from barstock and parted off. Holding the part to face the backside was a bit of a problem, not to destroy the knurling and to keep the faces of the part parallel.
I decided to make a pott chuck out of delrin with a light pressfit for the knurled part. The pott chuck was clamped in the three jaw chuck and allowed me to do all machining operations.
After machining, the part was pushed out from the back with a plastic punch.
The pott chuck has a register on front that sits directly on the face of the jaws of the three jaw chuck and it has a mark scribed to align it always with the first jaw - That ensures good runout even with taking the pott chuck out of the machine and reclamping it.

Quick way to make a radius grooving tool

Whenever I need a radius grooving tool for the lathe I try to find a piece of round Hss or Carbide with the right diameter that can be soldered on the end of a soft toolshank to form the radius cutting edge.
For the tool in this example I took a piece of unhardened toolsteel, machined a nose on the end, slightly narrower than the actual diameter of the Hss blank that gets soldered to it (I needed a 1,2mm radius on this tool, so I used a piece of 2,4mm diameter Hss and I machined the nose to 2,2mm with), then I machined a V-grove into the end of that nose to center the Hss blank. The toolblank was tilted by 5° to give the tool clearance without having to grind the actual clearance into it:

The finished toolshank with the 2,4mm Hss blank:

The Hss blank got hard silver soldered into the shank (Hss does not loose its hardness when silver soldered) and then ground sharp on the surface grinder (It could also done on the benchgrinder):

The 5° tilted round Hss blank alters the actual radius that the tool creates slightly, but in this case, the error is only 5/1000mm on the radius. It is quite easy to check this in a Cad program

The tool in use to machine a radius groove into titanium - The tool will only plungecut but not cut to the side, as there is no clearance to the side built into it:

Grinding external radius lathe tools

To grind a tool to turn concave radii, I rough out the radius on the benchgrinder using the edge of the grinding wheel. To finish the radius, I dress a grinding stone in my handheld rotary tool to the desired diameter and use it to finish the radius:

When doing this, I prefer to run the rotary tool quite slow to be able to press it tightly into the radius I want to form. Using a permanent marker on the surfaces to be ground shows you the progress.

Regrinding carbide inserts for special operations

In some cases it is benefitial to change the grind on an off the shelf carbide insert.
This part was such a case, it has to be turned down do a 3,9mm diameter, 17mm long. With a normal finishing insert it did not work very well, I could not hold any reasonable tolerance because oft the cutting pressure.

I did also not want to come back with a second tool for finishing, as I had to make a bunch of them.

I decided that a normal CCMT06 finishing insert with a 0,2mm nose radius is a good starting point, but I ground a substancial back- and side rake to the top of the insert.
That way I was able to rough and finish with two cuts - First cut took it down to 4mm in diameter, second cut finished it to 3,9mm +-0,01mm.

The way the insert was ground is very primitive: I grab them with a needle nose vice grip.
Then the the top face of the insert is held freehand against a diamond wheel, eyeballing the angles - I tipped the top surface about 5° back and to the right, to create a nice, positive cutting action with very little cutting pressure. As the insert has already a nose radius of 0,2mm, it is also a very durable tool.

I improved the way I grind/regrind the inserts by using the surface grinder - That way, they all come out exactly the same.
The procedure is shown in this video: Regrinding carbide inserts

Using a ball bearing to hold rough and non parallel parts in a vice

The purpose of the flat is to protect your vice.

By using the bearing ball on one side, you create a pointcontact situation against the workpiece and non-parallel surfaces are not an issue anymore.

Centering work on the rotary table

If your rotary table has a morsetaper socket in its center, a morsetaper collet and a pin can be a simple way to center a workpiece that has already a hole drilled in its center (Conrods for model steam engines are a good example where this technique works well.
The collet with the pin is just pushed by hand into the morsetaper of the rotary tabel and then the work is placed on parallels (to clear the collet) over the pin and clamped in place.