Metric drills and taps?

[Analias]

My CNC'd X3 (using CNCFusion's kit) is 98% metric bolts and measurements. I find I need to drill and tap mounting holes in a piece that anchors the Y-axis ball-nut to the base of the X3. Oddly, I have never contemplated metric drills, taps, or hardware. Is there such thing as a set of metric drill bits? What would be a good size set to pick-up?

I already have a 115pc standard set of drill bits. Is there the equivalent for metric?

If I was going to pick-up taps to have on hand, what sizes would be good to start with?

When I buy hardware (nuts, bolts, screws) I tend to buy a whole box when I only need a handful. That way I have build up a stock of hardware to use in the future. Like the question on metric taps, what sizes and lengths would be good to build up?

I expect I'll be focusing mainly on socket head hex screws and bolts. What grade would be appropriate for use with modifications, repairs, and maintenance of metal working tools (mills, lathes, etc.)?

As always, answers, comments, and factious remarks are appreciated.

 

[Ray C]

Most of the time, you can substitute an SAE-style bit for a metric size. Just go to a metric threading chart and some of them even will show the closest SAE size. The smaller the hole, the closer you want to get things but for holes upward of 3/8" (which is roughly an 8mm bolt) the world wont come to an end if you're a few thou off. Just remember there's 25.4 mm per inch so you can convert or use an online calculator.

If you want to get a good idea of which ones to keep on-hand, look at some basic sets sold by Irwin, Harbor Freight etc... they usually contain a good sampling of sizes.

My CNC'd X3 (using CNCFusion's kit) is 98% metric bolts and measurements. I find I need to drill and tap mounting holes in a piece that anchors the Y-axis ball-nut to the base of the X3. Oddly, I have never contemplated metric drills, taps, or hardware. Is there such thing as a set of metric drill bits? What would be a good size set to pick-up?

I already have a 115pc standard set of drill bits. Is there the equivalent for metric?

If I was going to pick-up taps to have on hand, what sizes would be good to start with?

When I buy hardware (nuts, bolts, screws) I tend to buy a whole box when I only need a handful. That way I have build up a stock of hardware to use in the future. Like the question on metric taps, what sizes and lengths would be good to build up?

I expect I'll be focusing mainly on socket head hex screws and bolts. What grade would be appropriate for use with modifications, repairs, and maintenance of metal working tools (mills, lathes, etc.)?

As always, answers, comments, and factious remarks are appreciated.

 

[Analias]

I don't necessarily want to replace the metric screws with the closest SAE size. I would rather keep a piece of equipment totally metric if it started that way.

Looking at the common metric tool sizes would be a good indication of the sizes for hardware I would need to keep around. Tools wouldn't have size ranges they do if they weren't in use.

 

[bushwacker]

If you know what the pitch of the thread is a rule of thumb to the siize to drill for tapping is subtract the pitch from the diameter and hey presto a size for drilling.

E.G. a 4.00 m/m thread is a 0.070 pitch subtract that from the dia and the tapping drill is 3.30 m/m a 4.50 dia thread is 0.75 m/m pitch subract that from the dia and the tapping drill is 3.75 m/m.

I hope that helps you.


Phillip.

 

[Ray C]

The point I was trying to make is that if need to use say a 7mm drill bit, you can convert that to decimal and use the closest SAE drill bit. You can indeed purchase a metric drill bit set. I have one somewhere but for all practical purposes, I've always been able to find an SAE drill bit that was darn close enough.


No, you should not contaminate SAE and metric sized bolts/screws/nuts in one machine. Good way to strip something...

I don't necessarily want to replace the metric screws with the closest SAE size. I would rather keep a piece of equipment totally metric if it started that way.

Looking at the common metric tool sizes would be a good indication of the sizes for hardware I would need to keep around. Tools wouldn't have size ranges they do if they weren't in use.

 

[Dubbie]

Coming from a metric part of the world, here is what I keep in stock.

At least a set of drill bits ranging from 1.0mm to 13mm in 0.5mm increments. That is about 26 bits. Then I keep the drill sizes for the recommended thread hole sizes eg 4.2mm for M5 etc. then lastly I keep some like 9.8 for drilling holes to be reamed. So I don't actually have a lot of sizes. Maybe only 40 or so. As far as taps go, I find that M3, M4, M5, M6, M8, M10 are really my most used. I also keep these size bolts and screws in stock in 4 different lengths each. That takes care of 95% of the stuff I do.

 

[Analias]

@Ray C - Ah, I gotcha. You saying that you can get close enough with SAE sizes to be the metric equivalent. Makes sense, if you are close to say .005" or better.

@Dubbie - Your comments sound like a good description for a newbie starter kit. I suspect no one makes one though. What grade of hardware are you using? Is it suitable for use with repairing or building metal working equipment? Do you need to go all the way to grade 12.9 for use on mills and lathes to maintain strength and rigidity?

 

[Dubbie]

I buy good quality drill bits from an industrial supply house. They don't work out much more expensive than the hardware store junk. Maybe 2x the price, but they stay sharp 10x as long. I cut mostly steel and aluminium with a little bit of stainless. A few cobalt bits are good in stainless- especially in the smaller sizes where you are running higher speeds and things heat up more.

 

[Analias]

I buy good quality drill bits from an industrial supply house. They don't work out much more expensive than the hardware store junk. Maybe 2x the price, but they stay sharp 10x as long. I cut mostly steel and aluminium with a little bit of stainless. A few cobalt bits are good in stainless- especially in the smaller sizes where you are running higher speeds and things heat up more.

Ah, I may not have been clear. Perhaps I'm using the wrong nomenclature. I was curious what grade (quality/strength) you were purchasing your metric nuts, bolts, and screws at. The Wikipedia page for hardware (http://en.wikipedia.org/wiki/Screw#Machine_screws under the "Metric" header) says that metric goes from 4.6 to 12.9. Metric 12.9 ~= SAE grade 8.

 

[Dubbie]

Ah sorry! Misread. I don't worry too much about strength as usually I use stainless screws. Someone else will have to help you there.