Reamer sizing?

[JOEPRO]

I have a crank lock tool im making which will have 8mm hollow dowels welded to a 5mm steel plate.

3d print example



This is to accept m8 bolts. But I would like to add a little clearance to the holes and ream them out with my pillar drill once welding is complete.

If I have a 8mm drill bit first - can I step up to say a 8.5mm reamer or is that too large a jump for a reamer? And do "straight" reamers have a small taper on them or is there a specific type / style I should be looking for in this application? I'm thinking that a normal twist drill isn't a great way of enlarging the hole.

 

[Morris]

Given it's for a bolt and "a little clearance" I would just drill it. 8.3mm should be ok.

 

[RWD3M]

Just how much clearance do you want? The bolts are likely to be less than 8mm in diameter so I would try one in an 8mm hole and see if you get enough.

 

[JOEPRO]

Just how much clearance do you want? The bolts are likely to be less than 8mm in diameter so I would try one in an 8mm hole and see if you get enough.

I want to target final ole size of 8.5mm

 

[RWD3M]

I guess it depends on what drills you have available. I would say 0.5mm is a bit much for a reamer but I could be wrong. If you have an 8.3mm (as @Morris suggests) or a 21/64" would be a better bet. Most reamers (certainly all the ones I have) don't so much have a taper, but more a bevel on the end.

 

[JOEPRO]

I just found this site which includes a drill calculator. It says an 8.4mm bit is required for a 8.5mm reamer

Reamer Drill Size Calculator – Calculator

ccalculators.co.uk