How straight is a drill blank? 1

[TED7]

Morning / Afternoon*

I need to know the straigtness tolerance for a HSS drill blank to DIN338, anyone able to point me in the right direction?
My copy of DIN338 is conveniently in German (which I can't read) and I can't make out anything to do with straigtness as it's more to do with the geometry of twist drills.
I'm looking at using a blank to form the basis of some locating pins for the reason that they are straight, hard and have the surface finish I require thus negating the faff of making some.

*Delete as applicable

Designer of machine tools - user of modified screws

 

[swall]

Someone once asked Bill (Grumpy) Jenkins, the SBC builder and racer, how straight push rods need to be. He replied that if they rolled on a piece of glass, they were straight. So, maybe if you roll a 30 piece sample of drill blanks on a surface plate, you will get some idea of how straight they are. If they all roll, then no problem. If some don't roll, then you will have to figure out tolerancing.

 

[Tmoose]

Are regular dowels too short?

http://www.grainger.com/Grainger/dowel-pins/pins/fasteners/ecatalog/N-8m0Z1z0nn6f

 

[TED7]

They all roll very nicely on my granite, I know if I use them in the design, they will likely work, but its nice to be know what kind of tolerance im working to.

I might take a handful to the metrologists and get a tolerance that way. Will give them something to do other than stick slip blocks together.

Designer of machine tools - user of modified screws

 

[TED7]

Tmoose, you squeezed that one in before I replied.

I need around 70mm plus a bit to sink into the tool. I also need a snug fit with the mating part (a stack of disks with holes in). I can get drill blanks in 6.9mm diameter which gives me 0.085mm calculated clearance (assuming a very straight pin).

Designer of machine tools - user of modified screws

 

[juergenwt]

DIN 338 refers to DIN 1414 for technical details. There you will find a table for Radial Tolerance (Tr) for any given diameter and length. Juergen

 

[juergenwt]

I should have mentioned - these tolerances are for finished drills. So if anything the tol. for blanks would be less.

 

[MikeHalloran]

Aren't drill blanks shipped in annealed condition?

For long, straight, and hard, I use ejector pins where possible.

Mike Halloran
Pembroke Pines, FL, USA

 

[TED7]

Mike,
I assume it's possible to get them in annealed but ours are certainly hard. I use them to make rivet punches and quite often grind them into locating pins.

Juergen,
My DIN1414 is in German as well (I suppose it's to be expected working for a German company). I managed to make out Figure 1 as a graph of tolerances against length and diameter. It looks like they are tight enough for what I need.

Designer of machine tools - user of modified screws