View Full Version : Too many questions at once, so I'll ask them all here

06-23-2010, 03:48 AM
1) I have a plate 3/4 x 14 x 14 that I want to clamp down on the milling table at 31.x degrees, and then again at 20.x degrees. What is a good way to do this?

2) How is it that a 2 flute drill gives a 3 sided irregular hole? I typically see this when I haven't drilled thru yet, and there is a bit of chatter or vibration going on. Today I was drilling 9/64 holes thru 1/8 SS sheet, with a piece of aluminum as backing. All the holes were round on top, but some were 3 sided on the bottom.

3) I want to make some kind of a diamond abrasive-based contraption for sharpening/honing the front edge of my carbide parting insert. Either because I've dulled the insert due to improper parting technique, or because most carbide parting inserts come with a more blunt edge for heavier feeds. Is there some kind of a diamond coated cylinder approx 1" diameter or so that I can chuck up in the mill or lathe? Alternatively, I could just get some diamond sandpaper and tape it to a cylinder. What grits would be appropriate?

Your Old Dog
06-23-2010, 06:54 AM
Trying to be helpful but admit to some tongue in cheek advice.

I'd take question #1 over to Frank Ford's place. I'd be surprised if he couldn't tell you how to do it.

For question #3, the wheels in the Drill Doctors are 1" diamond and they sell replacements for them.

J Tiers
06-23-2010, 08:18 AM

A drill has two flutes, call them "A" and "B". If the edge/corner at flute A "catches" in the hole, the flexibility of drill and setup allows the end to pivot around the "caught" flute, cutting a radius with flute B.

Then when flute B catches (as it is bound to do), flute A may break loose due to the changed angle, and pivot around B. now you have two "sides" of the triangle.

If flute A catches again, as is likely, it again pivots around B, cutting the 3rd side.

This tends to happen at 120 degree angles, +-, as that is where the system can keep working. Each rotation re-inforces the last.

The principle is used (with help from a guide) to cut square holes with a 3 fluted drill, 5 sided with a 4 fluted drill, and 6 sides with a 5 fluted drill. I don't think it extends well above that.

I have a drill for square holes, and it works well. The guide provides automatic locations for the flutes to "catch".

06-23-2010, 09:25 AM
I assume on #1 the plate will be flat on the table, but you want to rotate the square to various angles relative to the X-Y axes.

It somewhat depends on how accurate you need to be. If +/- a degree or so is close enough, you can probably achieve that with a good protractor. If, as your 20.x implies, you need accuracy to tenths of a degree, you'll probably want to use a sine bar. I'd establish a reference fence parallel to either X or Y and set the sine bar off that. Since I don't have gage blocks, I'd use an adjustable parallel set for height with a micrometer.

A.K. Boomer
06-23-2010, 09:30 AM
Well said JT,

I might add that this effect usually takes place when drilling thinner materials,

when used for deeper pockets the drill starts to stabilize this phenomenon due to more depth of the drills flutes spiral getting involved which breaks the pattern, the lesser degree flute spiral the thicker the material has to be to stabilize the hole being drilled (that is if your looking for a round hole)

06-23-2010, 10:22 AM
You need one of these
also there are other ones called a sine tables and compound sine tables, that are accurate to within tenths of a degree.


...........if there are other holes to be drilled in the workpeice ...drill them now ...as they will be useful for clamping.........other than that without knowing your tools and equipement ..i dont know ..you will have to put pictures up of your arrangements, so people here can advice on best practice.
As regards your three sided holes.

1. You must have the worked securely clamped to the table.

2. It would help if a Pilot hole was drilled.

3. Extend you quill to the maximum ..........grab hold of it ...if it rocks too and through .you have a POS chinese pillor drill...that is adding to the cause of this. ....there is a crude little bolt to take up some backlash on the side of the drill ...but it usually makes the quill very stiff, by the time you get rid of only a little bit of it, you end up slackening off and compromising.

4, So on a chinky drill you have to plan to drill with your quill extended by the least amount.

or look out for a good drill that isnt of the same old chinese design.

all the best.markj

06-23-2010, 10:59 AM
beanbag, what you need is a tilting table shown top left on this page http://www.use-enco.com/CGI/INPDFF?PMPAGE=449&PARTPG=INLMK3&PMITEM=418-4200

TJ handled #2 and for #3 just replace the cutoff tip and feed a little harder.

Dr Stan
06-23-2010, 11:15 AM
#1 has been answered.

For #2 try sandwiching the SS sheet between pieces of plywood. Ending up with a three cornered hole in sheet metal of any kind is a fairly common problem. Punching the hole is preferred, but not always an option.

For #3 I recommend buying a tool grinder and mounting diamond wheels. Like this one: http://www.google.com/products/catalog?q=baldor+tool+grinder&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&cid=15754040033600649103&ei=tSQiTOiVMYSClAf364Ez&sa=X&oi=product_catalog_result&ct=result&resnum=3&ved=0CDUQ8wIwAg#

I found a brand new one on Craig's List for $500

06-23-2010, 11:44 AM
RE the carbide parting inserts, I'm struck with the idea that this may not be the right thing.

I use these inserts in my parting tool, GTN-3's:


I can't see going at them with a powered diamond wheel. If it is slightly dull, use a diamond hand hone and give it a couple swipes. That narrow edge will get sharper in a hurry.

Second, these guys are not like the real sharp aluminum inserts. I don't think you can turn them into one, but I could be wrong about that. If you want sharp, try some HSS. The little blades I show on my parting page (link below) are pretty slick.

Last, parting likes to be fed hard. If you're having a lot of chatter issues, sharpening may help, but try cranking your feeds and speeds. I can't tell you how many times I have had horrendous chatter that completely went away when I really pushed it.

Oops, I said last but it wasn't. Last set of inserts I got off eBay are real crap. Must be some kinda import or something, they had no name.

Here's a page on parting:




06-23-2010, 01:49 PM
For #3, I'll answer before Frank Ford gets a chance.


06-24-2010, 05:35 AM
Thanks. I think #1 and #2 are sufficiently answered.

As for #3, I still don't have any idea what is the kind of grit that is required.

06-24-2010, 06:47 AM
120 grit is good.

I will give you another answer to setting an accurate angle of rotation.

Line the plate up at whatever constitutes zero degrees and clamp it lightly. Find the centre of the plate and centre punch it. Install a sharp dead centre in the spindle. Holding the plate in place with the dead centre in the punch mark align it to zero degrees and clamp.

Calculate the tangent for the angle in question. Wind the dead centre over to the edge of the plate. Multiply the tan by the radius of the circle that fits in the square. Crank the spindle in the axis perpendicular to the axis across the plate to the offset thus calculated and use the dead centre to mark the plate at the edge. That is your angle in respect of the centre of the plate. This method works for any angle up to 45 degrees at which angle Tan = 1 = radius.