3/5 of an inch forstner bit?

[JDuke]

I found a forstner bit on amazon that was listed as 3/5” but it’s actually a 15mm bit.

3/5 or 0.6 inches is closer to 15.24mm

Why you may ask do I want  a 3/5 inch forstner bit.  
I am making a copy of the base of a bentwood case for a singer sewing machine, and the hinges that they used were 0.6 inch or 3/5
And need couple holes in the back of the case that are right around 0.6 inch.

15mm is to small and 16mm is too big.

I did try to grind a 16mm steel bit down to 15.24 and it was enough that it took most of the teeth off the forstner bit.

I also have ordered a 16mm carbide bit, and am going to try grinding the carbide down a little bit to get to the 15.24 or 15.25mm diameter.

Anyone have any other suggestions on how to get a good flat bottomed hole other than the above?

Thanks in advance.

Duke

[fredhargis]

What about a 5/8" spade bit and grind it down? Cut the spur back some as well. Might be easier to get to .6" with it.

[jteneyck]

What about a 5/8" spade bit and grind it down? Cut the spur back some as well. Might be easier to get to .6" with it.

^^^^  Should be a pretty straight forward process and if you screw one up it's not a big loss.  

John

[JDuke]

What about a 5/8" spade bit and grind it down? Cut the spur back some as well. Might be easier to get to .6" with it.

That’s a thought, but I haven’t had much luck with getting clean holes with a spade bit, and wouldn’t grinding that much off take off the cutting part of the bit off?

[rschissler]

Just a couple holes, right?  I would use the 15mm bit, then use a large dowel wrapped in sandpaper, and sand off the edges enough for the hinge to fit. Use a marker on the inside of the hole, so you know what areas to sand off.

[JDuke]

Just a couple holes, right?  I would use the 15mm bit, then use a large dowel wrapped in sandpaper, and sand off the edges enough for the hinge to fit. Use a marker on the inside of the hole, so you know what areas to sand off.

If it was just a couple, I might do that, but I have 56 sewing machines and several of them would be better in portable boxes when looking for a new home.

I have also thought of making a router jig that clamps to the box and use that to enlarge the hole, but if I can find or make a forstner type bit I think I will be better off not going through several steps to make the same hole.

I suppose the other option since I have several, is to program my CNC to do it.

Duke

[jteneyck]

If it was just a couple, I might do that, but I have 56 sewing machines and several of them would be better in portable boxes when looking for a new home.

I have also thought of making a router jig that clamps to the box and use that to enlarge the hole, but if I can find or make a forstner type bit I think I will be better off not going through several steps to make the same hole.

I suppose the other option since I have several, is to program my CNC to do it.

Duke

If you have a CNC and the parts are easily indexed on it, then it's a done deal for me.  

John

[MarkSingleton]

Jig for a router bit is what I would use. But then, I have no CNC capability.

[tomsteve]

might want find a machine shop that can chuck the bit in a lathe and turn it to size.

[JDuke]

I have a metal lathe, I’ll just have to come up with a makeshift tool post grinder.