basically I've never used a tap & die set before, and wasn't sure if there was a best way to rethread something, or a better procedure... The bolt is fine, but the mounting plate is shot... It was a 6mm bolt, and I'm assuming I just need to go up a size to an 8mm, or just to SAE instead of metric, since a 1/4 bolt I have seems to be beafier.... do I need to redrill the hole first, what is the best way to start "tapping" If I'm alittle vague here it's 'cuz I'm out of my element and looking for help.... any quick how-to or pointers would be great thanks....

 

drill the hole out with the recommended drill size for the tap ur going to use, then put some oil on the tap and have at it till ur fully threaded through the hole.

putting oil on the tap before tapping it important, keeps the taps lasting longer.

taping it otu to SAE vs metric is entirely up to you.

 

how wasted is the threads in the piece in question? before drilling it out, i would try to just run the same size tap through it and see if you can just retap it or clean up the threads in it. and if that doesnt work, you can always drill it out for the next size thread. better to keep it original size than try to make something work....
kyle

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eddiebx &raquo;</TD></TR><TR><TD CLASS="quote">drill the hole out with the recommended drill size for the tap ur going to use, </TD></TR></TABLE>

what's the corresponding size?

I'm going to be using a 1/4" bolt, and a 1/4" tap, do I want to use a 1/4" bit? seems to me that I would want to use a step smaller, like a 15/64 or 7/32?

can I Use Marvel Mystery oil, or should I go buy tap oil (is there a specific oil to use)?

btw the 1/4 is fairly close the hole won't need to be drilled that far out, in fact I can put a 7/32 drill bit through the hole by hand.... (the threads are that wasted the walls of the hole are almost smooth...)

I know this probably seems simple to you guys who do this a little more often, but this will be the first time I've used a tap/die and don't want to make any mistakes... appreciate the responses so far, thanks...

 

On the tap or die, there will be a drill size etched into it. For example, a tap for M12x1.75 would say:

M12x1.75
drill 10.2

If not, there are references you can find online that will tell you what drill to use. The real pain of tapping threads is that you usually don't have the right size drill. Most people own fractional drills only, but many taps need metric, letter or number drills.

 

yeah, the tap says 1/4nc20 .... It's SAE, keeps me closer to the same size bolt then the next up metric (from 6mm) at least with what I have in hand....


how did you get drill a 10.2 from 12*1.75? just outta curiousity?

 

There are several correct sized drills for each tap too. depends on how precise of a fit you need. they range from about 60% to 100% thread. The deeper the threads the stronger so you might want to go with the smallest drill.

When you are cutting the threads cut a 1/2 turn then reverse for a little to break off the newely cut metal. You can use pretty much any oil. I use WD40 because its easy to spray on and i dont use it for anything else.

 

so with the roughly 7/32 hole I should be okay to cram the 1/4 tap through? or should I drill out with a 15/64 bit? will the tap thread out a hole 1/32 bigger?

thanks again....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by foz &raquo;</TD></TR><TR><TD CLASS="quote">
how did you get drill a 10.2 from 12*1.75? just outta curiousity?</TD></TR></TABLE>

That's what it says on the tap.

Anyway, within 5 seconds on Google I located a drill guide:

http://www.engineersedge.com/tap_drill_chart.htm

1/4NC20 means:

1/4" major diameter, National thread, Course, 20 threads per inch.

The drill size for this tap is a #7. If you want to use the closest fractional drill, look up the actual decimal size of the drill here:

http://www.engineersedge.com/drill_sizes.htm

So the 13/64" drill is your best bet that you can buy locally.

Good luck.

BTW, if you need to find any tap, I often buy strange taps at http://www.e-taps.com

Recently I needed a M12x1.75LH tap set and that is the only place I could find it!

 

thanks beepy, and everyone else, now I just need to start threading, I'm feeling much more confident now....

 

There are also different types of taps that can be the same size and thread.

Bottoming taps or Plug tap- I can't find a picture of a true bottoming tap right now, but it looks similar to the one on bottom in the picture below, in that it's not pointed on the end, but unlike this one, a bottoming tap for bolt threads will not have the tape this one does because it is a pipe thread tap.


This website says these three taps are tapered, plug, and bottoming taps, from top to bottom.

The bottoming taps are flat on the end and made to tap all the way to the bottom of a hole. It is not reccomended to use them for anything but to cut the lat few threads that the other tap types can't get to. These taps are usually hardest to start, and will also be harder to use since the first thread is the one that cuts all the material out of the hole.

Tapered tap-

These have a taper, of course. They will start in easier and it will be easier to get the thread straight. These taps will have about 10 threads that will each cut a small amount out of the hole...getting deeper as the tap goes in.

Gun tap-

There may be a better word for these, or a technical term, but this is the best kind you can get. Unlike the other two types, you DO NOT reverse the tap until you are at the bottom of the hole or have tapped as deep as you want to. These can be put in a drill and run in and out as fast as the drill can go. Should you want to tap all the way to the bottom of the hole, you will need to be sure to stop the tap before it hits bottom or set the tension on your drill so that it won't break the tap....then get a bottoming tap to cut in the last few threads. The reason for this is because the gun tap does have a slight taper, but not nearly as much as the ones I mentioned above.


All taps will work best with a lubricant.

 

good info

 

never knew about the gun tap. thats pretty cool, seems almost magical

 

lol one thing also, never trust what your carrying box sez the tap is, always read the shank.

i ended up tapping a ******* hole with a m11x1.25, m11 bolts are ******* impossible to find so i had to go with a 7/16"NF or someshit..

i know i am an idiot

 

The gun tap are awesome...well worth paying some money and getting a couple more common sizes.

They're the reason that machinists break few taps. They will work well in a mill or drill press, as long as you can reverse them quickly to keep them from hitting bottom or going to the end of the tap's thread.

If you have a 2 flute gun tap and are tapping something like 1/2" plate, it will "shoot" two chips out the far end as it cuts....similar to how a sharp drill bit will have two turnings twirling out as it cuts them.

 

What kind of bolts honda uses....fine or coarse?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Pete_SI &raquo;</TD></TR><TR><TD CLASS="quote">What kind of bolts honda uses....fine or coarse?</TD></TR></TABLE>

Both, depending on the particular bolt. Most that I've had to replace have been coarse, but there are at least a few fine thread bolts.

 

wow I had no idea there was so much to taps... great info!

 

I like to use a tapping wax instead of oil, especially in those situations where you want to "control" the shavings.

Also, if you have a drill press handy and arent confident in your ability to tap it straight. You can drill the hole and then replace the drill bit with the tap and hand turn the chuck for the first few threads to start it straight. Then just remove it from the drill press and use your normal method of tapping.

 

i need to tap and re-thread the hole that holds the engine mount on the timing belt side, the mount that actually attaches to the motor. anyone have any suggestions?

 

So let me just get things straight

when using a tap and die, you will always have to go up a size then the stock bolt because the hole is bigger correct ?

But when using heli coil you can use the same stock bolt right

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 90blackcrx &raquo;</TD></TR><TR><TD CLASS="quote">when using helicoil you can use the same stock bolt right</TD></TR></TABLE>
A helicoil is a clever way to "bush" a threaded hole. A stripped hole is tapped with a helicoil tap and a small coil like bushing is threaded in causing the thread to be the same size it was before it stripped, only stronger. At work we do a lot of aluminum aerospace parts and a lot of them have helicoils installed as oem.
When using a helicoil, the stripped hole is usually very close to the "drill" size for the helicoil tap. Helicoil taps have the letters STI marked on them. STI = screw thread insert.
Now, metric taps. The diameter is the first number. The second number is the pitch or the distance from one thread to the next. For your drill size, subtract the pitch from the diameter and that is the size you drill before you tap in mm.
Yes, gun taps are the ****! In machine tapping, that's about all we use.
HTH
chris