Hi Guys,

I bought the 7/16 threaded backlash mandrel from mudhole. I believe it is designed by Tom.
Today I drilled out some timber blanks with a 7/16 bit and when I went to slide the blanks onto the mandrel they wouldn't slide one. They are just a tiny bit to tight. I checked the mandrel with calipers and it is spot on what it says it is so I am presuming the bit isn't the 7/16 it says it is. It is an expensive bit so I am surprised.
Before I take the bit back I just want to make sure that I should reasonably expect a bit of timber drilled with a 7/16 bit to fit the backlash 7/16 mandrel.

G'Day Ben what you have is a size for size fit (transition fit) it will be tight .You need a clearance fit either a 12mm or a 29/64"bit to give you the clearance you require or maybe a bit more .Alternatively you could ream the hole with some sandpaper on a dowell mounted in a drill & run it up & down through the drilled hole until you have the clearance you require

Regards Baz

Bundeena
NSW Australia

Lightly running a file or reamer through the bore just a handful of times will do what you want.

..............

I generally always have to run a rat tail file through mine

Ron Weber

Thanks guys

I like the tight fit. I just turn the lath on with it chucked up in one end and slide it on. With the spinning action you can get it on with no problem.