Member postings for MikeK

I finally got around to making this. It has a few mistakes, but I almost finished it today.

I have the clamping screw chucked in the lathe right now with no good idea how I'm going to cut the 0.040" radius groove. I do have a small set of imperial radius gages with 3/64" being the closest, but it seems unlikely that I could grind an appropriate tool bit. Any thoughts?

Also, I accidentally reamed the moving jaw guide pin hole too large, at 0.251" or so. I wrapped a piece of brass shim around the guide pin and it looks like I should be able to press it into the jaw. Will this be alright, or should I go with high-strength Loctite?

Mike

Okay, the 1/8" end mill as a boring bar worked well to square up the bottom of the hole and bring the diameter to 0.374"

Now the silly story:

I got some 3/8" diameter neodymium magnets from eBay a while ago and made a bunch of really strong refrigerator magnets. They hold lots of things and have a nice handle.

The body is aluminum and the magnet just pressed into a 0.374" hole.

Then I read on a machinist's website that he increased the pulling power of his magnet by wrapping the one pole around to the front. Like a horseshoe magnet, but where one pole surrounds the other. At least that was his contention.

My setup is like this:

• An aluminum body just like my original fridge magnet.
• The business end is bored out 5/8" diameter to a depth of 3/8" (or so).
• A plug of mild steel is pressed into this hole and the whole thing faced off.
• The steel insert is bored out 1/2" diameter to a depth of 1/4" (the height of the cylindrical magnet).
• A plug of aluminum is pressed into this hole and the whole thing faced off.
• The aluminum insert is bored out 0.374" to a depth of 1/4" to expose the steel face.
• The neodymium magnet is pressed into this final hole and the back face (and only the back face) comes into contact with the steel insert.

This picture shows that one magnet pole comes directly from the circular face of the magnet and the other pole should be coming from the steel ring, separated by the aluminum.

The proposition is that instead of wasting the pulling power of one end of the magnet its lines of force are made to be redirected out front so that both N and S poles can be used.

I have not tested it with lifting a filling bucket of water to see how much it can lift versus the regular fridge magnet. But the seat of the pants test against the fridge says that both versions have the same pulling power even though a piece of ferrous metal is attracted to both the magnet face and the steel ring.

I don't want to use glue, because I want the magnet to be in complete contact with the steel at the bottom of the hole.

Thanks for that link, Anthony.

I decided to take the advice to use an end mill as a boring bar. Since I didn't have a way to hold the end mill securely, I made this tonight:

Thanks, Chris.

And I finally read the link Neil posted. It links to another page on how to make a D-bit. So I'll see what I can accomplish tonight. I'll post pics of the silly thing I'm using it for.

Okay, like this. What's a good angle to relieve half of the cutting edge?

Like this? I wasn't sure if the cutting edge should be relieved in two planes so the top view or the side view may be wrong.

Thanks for all the replies.

chris: Yes, the cutting edge for that bit was honed with a diamond hone. It may look dull, but it's actually quite sharp. I didn't know about milling to greater than 0.5 x diameter. Thanks.

paul, jason: Ohhhhhh! I didn't think to use end mill as a boring bar. Great idea! I need to try this!

Sorry, I should have given more information. The hole will be 0.250" deep and will receive a pressed-in magnet.

I've done this before with other magnets, but with those I made the hole deeper and used a 0.374" reamer. With this one I need the magnet seated firmly at the bottom of the 0.250" hole (and without thread locking compound).

I have this, but it's the wrong diameter and don't remember if it worked well. If I make one of the right diameter will it give me an accurate hole?

Edited By MikeK on 16/09/2015 13:07:19

HI guys,

So I need to create a flat bottomed 0.374" hole.

I know that drill bits create neither round nor accurately diametered holes and my smallest boring bar is too big for this task. I have made one D bit in the past, but don't remember if it created an accurately sized hole or not.

Should I make a 0.374" D bit, or should I make it a bit smaller? Or should I spend the time grinding a wee boring bar?

Thanks,

Mike

Regarding the "Small Instrument Vise" article in the recent anniversary issue...

Would it be alright to make this from cold rolled steel (1018) or even drill rod (what you Brits call "silver steel"?

I have plenty of 1/2" cold rolled steel. I also have 3/4" drill rod, but I imagine it'll take considerable work on my mini-mill to get it down to 1/2" square.

The article mentions "bright mild steel" and "EN8". I know nothing of such concoctions.

Mike

Thanks gents.

Like this?

I have the recent 25-year anniversary issue and in Harold Hall's article about the grinding rest he describes a method for cutting dovetails.

I'm a little confused by it. It seems to indicate that a dovetail is to be cut at two different depths, instead of going with full depth from start to finish. Is that right? Is this done to minimize cutter load?