Going from a 5mm to a 6mm hole

[Wamsutta]

What size drill bit would you use and which size reamer? I want the hole to fit a 6mm screw pretty snug.

The material is steel and it's about 1/8 inches thick.

 

[FigN⋅m]

30 sec with a chainsaw file?

 

[mikey03]

I would honestly take my SAE drill bit set, find the first drill bit that doesn’t fit the existing 5 mm hole which looking at my chart would he 13/64 but I would just test them by hand. I would drill the next hole and try the screw. If it was still too tight to fit it, I would go up one drill bit size. Repeat.

looks like 7/32 is 5.5 and 15/64 is 6 so prob one of those two would work. My drill bit set goes in 1/64 increments tbh

 

[dutchgray]

I would normally allow 2% for machine reaming in steel, which for 6.0mm is a 5.88mm drill, so I would probably use a 5.9mm since you already have a 5mm hole, but with no start hole I would probably test a 5.8mm and see what it actually drills at.

You should measure the screw your going to use though to see what it actually is and not just assume it's 6mm.

 

[RoninB4]

You should measure the screw your going to use though to see what it actually is and not just assume it's 6mm.

-This is where you should begin. Commercial grade fasteners are NOT to stated size, they're usually a few .001's of an inch (0.0254 mm's) undersize to fit a commercial sized tapped hole. If you're not using a micrometer to measure both the screw and the drill then you're just guessing or asking others to guess. You also haven't stated whether hole size or location or both are important. You could also do the math converting metric to inch (it's easy) and find an appropriate drill in inch that will likely work for you if you'll define what "pretty snug" means. Limited movement in the hole? Light tap fit? A reamer may not be needed but you'll have to define the application better for a better answer.

 

[mjdarg]

Do you need your hole to be 6mm or 6.00mm? Are you doing this in a milling machine? If you're just doing this for a tight fit with a 6mm screw, I would measure the actual diameter and select a drill bit based on that. If the screw has a shoulder, that will add a few thou to your measurement. Drill bit holes can be a few thou over depending on the setup and how its drilled too. 15/64" would have a pretty good fit for a 6mm screw, but it depends on the major diameter of the threads or if its got a shoulder.

If you need it to be 6.00mm, I'd get a 6.00 mm chucking reamer and drill it with maybe a #1 bit, leaving 0.004" on the radius to be removed by the reamer. You can play with final reamed hole size by feeding slower or quicker if you really need to dial it in. In and out quickly and you can maybe get it slightly under 6.00mm.

 

[AEAdam]

Really good chart ^^^^ Good responses. Quick answer is 15/64", which is just under 6mm. Assuming the major die of a 6mm bolt is just under 6mm

 

[JradM]

I liked this discussion. It's entirely academic to me. When I'm trying for a tight fit on a fastener, I just sneak up on it - maybe grab a reamer if I want to refine it to the last thousandth.

Of course there's a better way to do it. I also appreciate drill bits drill oversize. I just can't imagine a situation where I would "do the math" as opposed to trial and error. Even if it were multiple holes, I'd trial-and-error the first one and then proceed with the right size for the rest.

This is in the home shop of course. I appreciate production items might be junk if insufficiently precise.

 

[Monte]

step drill bit

 

[OccupantRJ]

You can take a rat tail file, remove the handle tang, chuck it in a drill, run it in REVERSE, (LH) and put the size right where you want it, especially in 1/8” material. Left hand rotation keeps it pushed back out of the hole instead of grabbing. One of the best devices I ever came up with. I have three different sizes ready to use.

 

[vwpieces]

step drill bit

+1

 

[PCustoms]

step drill bit

+1

How is that supposed to work any different then a normal (correctly) sized drill?

I suspect tre OP has no reason for a reamed hole with a off the shelf screw. This post is the answer:

I would normally allow 2% for machine reaming in steel, which for 6.0mm is a 5.88mm drill, so I would probably use a 5.9mm since you already have a 5mm hole, but with no start hole I would probably test a 5.8mm and see what it actually drills at.

You should measure the screw your going to use though to see what it actually is and not just assume it's 6mm.

 

[vwpieces]

How is that supposed to work any different then a normal (correctly) sized drill?

I suspect tre OP has no reason for a reamed hole with a off the shelf screw. This post is the answer:

for one it meets the parameters of accuracy set by the OP

I want the hole to fit a 6mm screw pretty snug.

1/8in material and a fluted drill actually making a round hole? Good luck.

 

[AEAdam]

step drill bit

huh? can a stepped drill really move you from 5mm to 6mm? Couldn't you slip and end up with a 1/2" hole? I didn't think the steps were small enough for that. Gotta link? I think of stepped drill bits for crappy holes in sheetmetal.

 

[garfunkle24]

Might be hard to find correct sizing in a step drill but they drill way rounder and closer to size than a twist drill in that material thickness.

I also have several step drills in 1mm increments and one that is 0.5mm increments (pre-Irwin OG Unibits).

They make for decent spotting drills too.

 

[PCustoms]

Might be hard to find correct sizing in a step drill but they drill way rounder and closer to size than a twist drill in that material thickness.

I think we're looking at this from a machinists perspective when the OP just wants a 6mm bolt (threaded shank? Shoulder? Shcs?) to fit "snug". Unless I missed that definition in the handbook, the OP can likely grab a 15/64th bit and be more then happy.

How precise does a shopping cart axle need to be anyway?

 

[garfunkle24]

I think we're looking at this from a machinists perspective when the OP just wants a 6mm bolt (threaded shank? Shoulder? Shcs?) to fit "snug". Unless I missed that definition in the handbook, the OP can likely grab a 15/64th but and be more then happy.

How precise does a shopping cart axle need to be?

Yeah if it were mine that hole would already be drilled with a 6mm step drill and I'd have moved on to extensively researching hair removal tooling.

 

[PCustoms]

Since it keeps coming up, anyone ever measure a step drill for size?

Are there precision step drills?

 

[vwpieces]

Since it keeps coming up, anyone ever measure a step drill for size?

Are there precision step drills?

Doubt any Machinists, Engineers or Rocket scientists can dispute accuracy of a Mitutoyo caliper.

 

[Dave455]

Just a small observation, as I know most folks here are not too familiar with metric.

With a UNF or UNC thread (or a BSF, or BSW) the bolt / screw is normally slightly under the nominal size. When you tap a hole, the tap will be the exact size, giving enough clearance to turn the screw.

Now, the question for the O.P. is - what sort of 6mm?

If it’s an old one, S.I. metric or one of the old national standards, then the same applies - the screw will be a bit undersized.

But… ISO metric is different. An ISO metric 6mm screw will measure 6mm, give or take. An ISO metric tap will be slightly oversize, so the tap provides the clearance to turn the screw. The clearance hole will therefore need to be bigger than 6mm. ISO list two clearances - a close fit needs a 6.4mm and a normal fit 6.6mm.

In practice, not all ISO screws meet the standard, and some, particularly from the far east, tend to come out undersize. I just measured one or two reasonable quality ones from my stores however, and they’re averaging out at 5.97mm, so less than .001 undersize!

 

[JradM]

Just a small observation, as I know most folks here are not too familiar with metric.

With a UNF or UNC thread (or a BSF, or BSW) the bolt / screw is normally slightly under the nominal size. When you tap a hole, the tap will be the exact size, giving enough clearance to turn the screw.

Now, the question for the O.P. is - what sort of 6mm?

If it’s an old one, S.I. metric or one of the old national standards, then the same applies - the screw will be a bit undersized.

But… ISO metric is different. An ISO metric 6mm screw will measure 6mm, give or take. An ISO metric tap will be slightly oversize, so the tap provides the clearance to turn the screw. The clearance hole will therefore need to be bigger than 6mm. ISO list two clearances - a close fit needs a 6.4mm and a normal fit 6.6mm.

In practice, not all ISO screws meet the standard, and some, particularly from the far east, tend to come out undersize. I just measured one or two reasonable quality ones from my stores however, and they’re averaging out at 5.97mm, so less than .001 undersize!

This is a great argument for not "doing the math" and instead just grabbing your drill index for a little trial and error.

 

[PCustoms]

Just a small observation, as I know most folks here are not too familiar with metric.

I live in metric, every day, to extremely tight tolerances.

With a UNF or UNC thread (or a BSF, or BSW) the bolt / screw is normally slightly under the nominal size. When you tap a hole, the tap will be the exact size, giving enough clearance to turn the screw.

Now, the question for the O.P. is - what sort of 6mm?

If it’s an old one, S.I. metric or one of the old national standards, then the same applies - the screw will be a bit undersized.

But… ISO metric is different. An ISO metric 6mm screw will measure 6mm, give or take. An ISO metric tap will be slightly oversize, so the tap provides the clearance to turn the screw. The clearance hole will therefore need to be bigger than 6mm. ISO list two clearances - a close fit needs a 6.4mm and a normal fit 6.6mm.

In practice, not all ISO screws meet the standard, and some, particularly from the far east, tend to come out undersize. I just measured one or two reasonable quality ones from my stores however, and they’re averaging out at 5.97mm, so less than .001 undersize!

I don't think the OP was asking about tapping threads, so this isn't relevant.

 

[Dave455]

I live in metric, every day, to extremely tight tolerances.



I don't think the OP was asking about tapping threads, so this isn't relevant.

It is relevant.

Compared to other standards, the clearance hole for an ISO metric bolt needs to be a bit more above nominal size.

I was just trying to explain why.

And I gave the book figure - 6.4mm.

 

[ronkz650]

Get a 115pc drill bit set. Covers every size. As the post earlier showed, there are quite a few bits in the close proximity to 6mm. I love my 115pc set. Never have to file a hole.

 

[Monte]

https://www.amazon.com/Hyamass-Step-Drill-Drilling-Stainless/dp/B0CQQBKW26/?tag=atomicindus08-20

 

[RoninB4]

With a UNF or UNC thread (or a BSF, or BSW) the bolt / screw is normally slightly under the nominal size. When you tap a hole, the tap will be the exact size, giving enough clearance to turn the screw.

-Just to add something to your knowledge, the UNF. UNC, UNEF, or other thread designations can have up to 3 different class/grade tolerances that can be to stated size. A 1/2-20 3A or 3B can have a major diameter of .500 and be within tolerance. What's the lesson? Measure what you have not what it's "supposed to be".

But… ISO metric is different. An ISO metric 6mm screw will measure 6mm, give or take. An ISO metric tap will be slightly oversize, so the tap provides the clearance to turn the screw. The clearance hole will therefore need to be bigger than 6mm. ISO list two clearances - a close fit needs a 6.4mm and a normal fit 6.6mm.

In practice, not all ISO screws meet the standard, and some, particularly from the far east, tend to come out undersize. I just measured one or two reasonable quality ones from my stores however, and they’re averaging out at 5.97mm, so less than .001 undersize!

-You've just added to my knowledge (thank you), same lesson applies to metric it seems.

-For those of you that "can't imagine" doing the math......if poke-n-hope works for you then that's fine too. For the members that implied that using a twist drill in thinner material may not produce the hole you expect, they're correct. What will likely happen is a 3 lobed hole that's not truly round and probably undersize.

-Chucking a rat tail file in a hand drill running in reverse may work for you, I'd seek a different solution but you do you if you've convinced yourself. JMO

 

[Dave455]

-Just to add something to your knowledge, the UNF. UNC, UNEF, or other thread designations can have up to 3 different class/grade tolerances that can be to stated size. A 1/2-20 3A or 3B can have a major diameter of .500 and be within tolerance. What's the lesson? Measure what you have not what it's "supposed to be".

-You've just added to my knowledge (thank you), same lesson applies to metric it seems.

-For those of you that "can't imagine" doing the math......if poke-n-hope works for you then that's fine too. For the members that implied that using a twist drill in thinner material may not produce the hole you expect, they're correct. What will likely happen is a 3 lobed hole that's not truly round and probably undersize.

-Chucking a rat tail file in a hand drill running in reverse may work for you, I'd seek a different solution but you do you if you've convinced yourself. JMO

Yes, I was aware of the different classes of fit. I didn’t want to confuse things further.

Measuring what you have, and applying your own clearance, can never be the wrong thing to do! Especially in our world. If you’re specifying fasteners for a rocket or something, maybe not!

Like most folks here I suspect, I tend to think in inches, especially in small sizes. But I have to admit, the ISO metric system is incredibly easy to use.

 

[AEAdam]

I do NO metric, so I didn’t know you could have a 6mm thread with a major diameter bigger than 6mm.

 

[whateg01]

...
Measuring what you have, and applying your own clearance, can never be the wrong thing to do! Especially in our world. If you’re specifying fasteners for a rocket or something, maybe not!

Based on my initial reading of the OP, it seemed like op wants to use the bolt for location. I sure hope that's not what space x engineers are doing!

 

[Dave455]

Deleted

 

[Dave455]

I do NO metric, so I didn’t know you could have a 6mm thread with a major diameter bigger than 6mm.

In fairness, I suspect 6mm is the upper end of the tolerance.

 

[rust in the eye]

What size drill bit would you use and which size reamer? I want the hole to fit a 6mm screw pretty snug.

The material is steel and it's about 1/8 inches thick.

A bit more than 6mm then.

 

[Hannahranga]

step drill bit

Same, I'm not sure what we're missing here. Admittedly I'm an Aussie so all my stuff is metric.

 

[RoninB4]

Based on my initial reading of the OP, it seemed like op wants to use the bolt for location. I sure hope that's not what space x engineers are doing!

-While on contract assignment at Denso Automotive (Nippon Denso) a young degreed engineer had specified hole tolerances (.** mm) for exactly that reason/purpose of replacing dowel pins in an assembly. It wasn't for a rocket, it was automotive tooling but thought he'd made a breakthrough in mechanical design. Sometimes it's ok to do that, this wasn't one of those times.

 

[Ohio Andy]

I have a set of vortex point drill bits now. Admittedly, mine are SAE not metric but the principles the same, the point allows you to stick it into a smaller hole and when you're done you will have the proper sized hole and it will be appropriately centered

I got to say my Cobalt set is amazing ing. If you don't have a set you should get them.

 

[cherrybomb]

The Grainger catalog had a page that showed metric,sae,letters and numbers driil bits,I had a situation where I needed a roll pin in a steering part on my old lawn tractor.I bought 3 pins,there cheap,measured the squeeze, took a guess,bought two bits of different sizes.Hit a home run.
A little bit of study sometimes is a problem solver.I'm wishing I had that 115 piece set like previously reply