Tapping instruction please!

[Nima]

Well, some of you know the story; Bolt broke in the head, I drilled out and try to tap it, tap broke in the hole!. I spent all Sun and Sat try to fix it. I bought different type of extractors and etc. Anyways, Now I am at this point; I drilled the tap almost out but the hole is slightly bigger, ofcourse. Now, I would appreciate if somebody explaine to me how to do the tapping correctly. Please explain it in very simple language.
Also, I have another question, is there any product that I can fill the hole with and make smaller hole again! or should I just go with the bi hole.
I appreciate the time. Thanks.

[sdkid]

The hole can be made smaller(provided the hole is not to large already). Go to your parts store and get a heli-coil set. Look to spend about $50 for a complete set. Note, set means all the items needed to repair one thread size.

To tap: The tap has a drill size the corresponds with it. It may be etched ontop the tap or there may be a chart included with the tap set. Drill to the correct size. Insert the tap and coat it with cutting oil. Turn it in with the tap wrench, only 1/2 to 3/4 turns at a time. back it out to clean the tap of metal shavings. Repeat this to the desired depth. Clean the hole with parts cleaner or air pressure.

Hope this helps...

[hotrodtroy]

What sdkid said, but keep your tap well oiled.

[Nima]

There is a size for tap, I undrestand that but I don't undrestand the corresponding drill number. For example for tap size 1/4-20, the drill size is 7. What is drill size 7? By the way I have a craftsman set, if that changes anything.
Thanks.

[beautimus]

there are several measuring systems for drills.
the most common are fractional sizes, you can find them at any hardware, building supply etc.
then there are letter sizes, a, b, c, d, etc.
and lastly there are number sizes.
for number and letter sizes you will have to go to napa, or a place that sells to the machinist trade or some of the full line auto parts places, they are a little harder to find than a fractional size bit , but they are out there.

[68LSS1]

Here's a link to a tap/drill bit size chart. It is a .pdf file. If you haven't opened the hole or oversized it then yes you can use a helicoil like mentioned in the above posts. If you have oversized the hole (which sounds like you have) then tell me what size the hole is and I'll tell you what you need to do. With the hole being oversized the original size helicoil won't work. Which accessory will be using the bolt that goes here? It may be possible to fill the hole with something like JB Weld or Metalset as some of those products advertise that the material can be drilled and tapped but I wouldn't trust it. I'd oversize the hole even if it meant having to run a drill bit through a alternator ear or what ever.

[Tx Firefighter]

That's a 1/4-20 bolt you're dealing with.

As long as you haven't oversized it a whole lot, a normal 1/4-20 heli-coil kit will fix it fine. The kit will come with a tap and a install toool along with the heli-coil inserts.

Just drill the hole to the specified size and tap it with the tap. Screw the insert in and you're done.

By the way, no way it should cost 50 bucks for a heli-coil kit. Around here, they are right at 20 bucks.

[68LSS1]

Nima, was the 1/4-20 just an example or is that the size of bolt hole your working with?

[Nima]

Sorry about writing late, I had problem with computer at work (I am suppose to be at work now). Anyways, If you don't laugh at my lack of knowledge, I have to say I don't know the actual original size of the bolt. It is for Vavle cover, they seem to be all original. I used 7/16 socket to open them and they are about 1/2" tall. Now, I used a drill bit size 15/64 to drill it. Original bolt is slightly loos in it but 1/2" bolt doesn't fit in it. Again I am sorry if I can not give you more accuarate info. If you lead me. I'll be able to give you the specifications.
Thanks for taking time.

[68LSS1]

To make it easier I'll convert the drill bit sizes to decimals. The drill size for a 1/4-20 tap is a #7 bit which is .201. The 15/64 bit you used is .234 so you've oversized about .033". You should be fine to get a 1/4-20 helicoil kit and go ahead and tap it and insert the helicoil. Just make sure it is 1/4-20 which is course thread and not 1/4-28 which is fine thread. Bolts/screws, etc. are sized by their diameter not the head size. Tx Firefighter is right in that the valve cover bolt should be a 1/4-20 and a kit should be about 20 dollars that will include a bit, tap, insertion tool and 5 to 10 or so helicoils. Just be sure to use some sort of cutting oil with the tap and keep the tap perpindicular with the hole.

[Nima]

Thanks for detailed explanation.

[sdkid]

I gotta find a new parts source. I paid over $40 for the last heli-coil set I bought. And yeah, like they said, keep plenty of cutting oil on it.

[68C15]

go slow with the tap. it takes less time to do it slow & easy than it does to deal with a broken tap. it is something you kind of get a feel for with practice.
if the metal is rather hard & or the item being fastened doesnt require lots of clamping force you can go a little oversize with the drill bit. (it has to do with the depth of thread, 60% 75% etc.){but this only applies to normal tapping, not doing a helicoil}
sdkid, that's the price you pay for living in Pierre. JK

[Nima]

Do you have any part number for helicoi? Unfortunately what I found on the internet was only part numbers and the guy at auto part close to me was not that much help. Thanks

[chickenwing]

I have never found em out here with the bits included. I pretty much only shop Napa, Autozone and Kragens though. I looked up Napa's part# for you. BK7703044 $26.99. You would still hafta buy the bit and I bet they want around 4-5 bucks for that. If anyone has a vendor in his area with a cheaper price sound off. Oh, and the part was made by Belkin or Balkamp.. Dunno if that makes a differance in quality.

[68LSS1]

Hc5521-4 is one part number. I messed up with the link for the tap sizes. Those would be for tapping threads without a helicoil. For a helicoil kit for a 1/4-20 you will need a 17/64" bit and this kit which is under 20 dollars. Here is a helicoil tap/drill chart.

[chickenwing]

Buy the time he paid freight, he would probably be even with the napa price. Great site though. I bookmarked it.

[68LSS1]

Originally Posted by chickenwing

Buy the time he paid freight, he would probably be even with the napa price. Great site though. I bookmarked it.

Agrred but that is to show him exactly what he is after and give him the exact part number, helicoil part number anyway. I'm sure some vendors change them. He should be able to find one local for about the same price. Nima, you might call a couple local machine shops to see where they get their stuff.

[LONGHAIR]

The "plenty of oil" reccommendation is fine for steel...........
It doesn't work that way for cast iron though. The cast iron is to be drilled and tapped totally dry. The chips come off like powder and oil gums up the works. A little air blown down the hole wont hurt anything, but no oil.

There is a special lube for tapping aluminum too......but you can use rubbing alcohol in a pinch

[Nima]

Thanks guys. I ordered it since I wouldn't have time to work on it until next weekend anyways. With everything, it cost less that 24 $. I hope I won't mess it up!. You will hear from me.

[chickenwing]

Right on! Don't forget the 17/64" bit 68LSS1 told ya about.

[LONGHAIR]

Just because I know that someone is gonna think I'm nuts........

http://popularmechanics.com/home_imp...s/index4.phtml

I learned this in my machinist class in Tech School....but I had to search a while for on-line verification.

[kw]

Something else when tapping holes. Go in a little bit, back it out and clean the tap. Go back and cut a little more, working the tap back and forth a small bit. In other words, don't try to tap the entire hole all at once. Chips will break off and gather in the flutes. If you go slow and use this process in addition to what other board members have told you, you should be all right. Blow it out often so the tap doesn't bottom on a pile of chips.

Take your time and you should be OK. This applies whether you are tapping the hole or tapping for a helicoil. If using a helicoil, remember to break off the driving tang at the bottom of the insert after installing. A good sharp whack with a punch will usually do the trick.

Good luck.

[68LSS1]

Longhair, good tip not using lubricant with cast metal. I didn't know this. I knew about the alcohol as that is what we use at work all the time with aluminum.