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Most common drill bits to use for the most common taps?

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Pcmaker

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#1
Which tap sizes are used the most and which drill bits do you need to tap the threads? I'm going to buy packs of cobalt drill bits from Amazon since they're not so expensive over there. The ones I've seen are metric for some reason.
 

ELHEAD

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#2
Hey , Pc Just google tap drill chart . You should find one you can download, or print pdf.
Dave
 

JimDawson

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I like the Harbor Freight 115 piece cobalt drill set. About $120 full price, but wait for a 20 or 25% off coupon. That will cover all of the tap sizes from #0 to 1/2 inch. They are actually high quality drill bits, made in Russia I think.

For taps, it depends on what you are doing, but I use 10-24, 1/4-20, and 3/8-16 the most. Buy good taps, I normally buy spiral point taps from Fastenal. Have had really good luck with those. I think Fastenal sells OSG taps with their label on them.
 

royesses

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#4
Here are two good tap drill charts from LMS with 50% and 70% tap drill listings and clearance hole drill listings in metric and US fractional sizes. You can choose the sizes you would use the most. I have the HF cobalt drill set that Jim Dawson likes and it is really good. I also have metric drills in.1mm increments for 1 to 5mm and .5mm increments from 5mm to 13mm. They can get expensive. I also have screw machine length sets for use in close quarters work or try to get a closer approximation of a round hole. It takes a while to accumulate all the drill bits you may eventually need or want.
You may need letter drills or number drills which are in the HF cobalt set.

Roy
 

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markba633csi

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#5
I use the smaller sizes a lot: 4-40 to 10-32 and metric from 6mm to 10mm
I have a number drill set, a letter set and a fractional set (but I didn't buy them all at once):grin:
mark
 

BaronJ

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#6
Hi Guys,

Maybe you already know this, if you are stuck for a particular drill size, go to a slightly larger drill. For instance for M9 you need 8.4 mm, but 8.5 is a standard size. That LMS table is nice because it lists both 70% and 50% tapping drill sizes. Don't go below 50% thread engagement if you can avoid it. This becomes more important with smaller sizes. You are less likely to break a tap if the hole is larger.
 

Mitch Alsup

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#7
I like the Harbor Freight 115 piece cobalt drill set. About $120 full price,
This is the set of drills to have:: a) cobalt drills b) at lower than HSS prices.
 

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PT Doc

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Creativechipper

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I think I will go to HF and inspect them 1st after this set I got blind..lol

I couldn't believe how bad of a finish and dull plus plating issues too.

So a good set of HF cobalt drill bits vs titanium bits should be good?
 

JimDawson

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I think I will go to HF and inspect them 1st after this set I got blind..lol

I couldn't believe how bad of a finish and dull plus plating issues too.

So a good set of HF cobalt drill bits vs titanium bits should be good?

That's been my experience. In fact I have a 20% off coupon and I'm going to go buy another set to add to my collection. I usually buy a couple sets per year, just to keep my stock up. I quit buying the TiN coated ones, the quality is not as good as the cobalt.
 

PT Doc

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That's been my experience. In fact I have a 20% off coupon and I'm going to go buy another set to add to my collection. I usually buy a couple sets per year, just to keep my stock up. I quit buying the TiN coated ones, the quality is not as good as the cobalt.
I said that a bit tongue in cheek because it sounds funny to me at least to say that someone should just have gone out a bought a quality set AND bought that at hf. The cobalt set is supposed to be good though.
 

royesses

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I purchased my set of HF cobalt's about 6 years ago. Hopefully they have not changed suppliers. I open the set in the store and looked at all the bits as though I was doing a QC check. They looked very good. They are 135° split point. They have far surpassed what I expected. The cobalt set is the only one I would purchase from HF. The other sets look awful to me. I have precision twist drill, Cleveland and other sets but the HF cobalt's are my go to. When a bit breaks I replace it with a decent brand. I've replaced 2 bits in 6 years. 1 was my fault for getting the bit cocked and bent(#50 bit in a hand drill) and the other my son broke drilling out a small hole in diamond plate. I watched him and told him he was putting a side load on the bit and just then it snapped (1/2" bit). He tends to break things like breaker bars, pipe wrenches and any tool that isn't an anvil. That bit I had used to drill out cast steel lower control arms for his friends 3/4 ton 4x4 and the bit cut them like butter. Not trying to say that HF drills are the best, just that the cobalt 115 piece set is a great buy with a coupon.

Roy
 

jdedmon91

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#15
Another thing I seen a is estate sales. A lot of older folks have assorted drills, sometimes you can get them cheep but more than likely you’ll need to sharpen them.

I have an odd collection that someday I finish sharpening and sorting


Sent from my iPhone using Tapatalk
 

Pcmaker

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#16
Can't believe I messed up. I am replacing my compound slide with a thick block of steel. I bought some M6-1.- from Home Depot as fasteners.

I used 6mm drill bits to drill 6 holes through the cross slide and the 1.5 inch block.

I'll go up to M7-1.0
 

Ken from ontario

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#17
I would go with M8x1.25 , could find M8 bolts very easily.
Drill size 6.7mm.
 

BaronJ

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#18
Hi Guys,

An easy mistake to make ! I've done it myself on more than one occasion. Nowadays I have a big A1 chart hanging on the wall, :D

As others have said, redrill for M8 X 1.25.

If you are really desperate to use M6, then get some thread inserts.
 

BGHansen

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#19
Not adding anything new here, but I keep my taps in plastic storage bins and have the recommended drill bit size in the same bin. If it needs a tighter or looser fit, I look at the drill chart and go up/down a size accordingly.

Tubalcain has a nice organizer idea with the typical tap drill, clearance drill and tap in a block. Just make sure you grab the tap drill and not the clearance drill.

I've had very good luck with the HF cobalt drills mentioned above, have sets of those at each lathe. Naturally, a lot depends on your projects. If you're going to do a boatload of 3/8"-16 holes, buy some good 5/16" drill bits (tap drill for 3/8"-16). It's frustrating pulling down hard on the quill handle without seeing any chips.

Bruce
 

Ken from ontario

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Tubalcain has a nice organizer idea with the typical tap drill, clearance drill and tap in a block. Just make sure you grab the tap drill and not the clearance drill.
I actually followed Tubalcain,s tap/drill organizer idea and made one very similar to it, makes my life much easier , now I always know I have the right size tap and /or drill bit in my hand.
 

NortonDommi

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#21
+ 1 BGHansen,
Having a dedicated bit with the taps means no searching, looking for a magnifying glass when wearing the wrong glasses to check sizes etc. I buy good quality Cobalt bits when and as needed whenever I buy new taps. Common sizes I might have bits for a loose or tight fit depending on material, use.
I am replacing/updating some of the more used taps when on special with Voelkel serial taps. I love these for ease of use in hard or tough/'sticky' material otherwise it is spiral flute gun taps.
https://www.voelkel-shop.com/en/voelkel.html
 
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