Hole Threading - Help a newb

[porphyre]

Ok, so I broke a couple bolt heads off and the stud extraction process was a disaster. Therefore, I now have a few 1/4" holes with no threads.

I know just about zero about tapping and drilling. Don't own any taps, etc. What do I need to do to get threads into these holes? I looked up a tap drill chart and don't see .250 listed as a drill size. .250 is close to "F". Can I use a 5/16-18 tap in my 1/4" hole?

Material is plain steel. Thickness is probably just under 1/4". The holes will be very very light duty - they'll hold screws that hold on a plastic undercover on my car.

Thanks for any help.

 

[Walterchang]

You have a couple options. 1 is to use a helicoil. It is very easy to use, just read the instructions and do a practice one first. Helicoils require a larger hole that is tapped, then insert the helicoil, break the tang, then use the appropriate size fastener.

Option 2: tap the hole that you made and use a larger fastner.

Option 3: use a large bolt and just force it. Not really an option,

 

[toolman1967]

If you are ever in doubt about what size drill to use for a given tap, just hold the tap up and put the drill bit behind it. If you can see the threads and just a bit of the bit at the bottom of the threads, you are pretty close. Personally I use a tap/die thread chart in my Machinist handbook. That was the schooling answer, short answer, YES.

 

[mike13u]

Your going to have to make the hole a 5/16 hole and use 5/16 fasteners or use Helicoil. If you can afford to make the hole next common size up (5/16), then go to your hardware store and grab one 17/64 drill bit and one 5/16 tap (fine or coarse. hint: if you have never tapped use coarse). You will also need a tap wrench to hold the tap. All that should be less than $20. Tapping is easy. Drill your hole to 17/64. Hold the tap verticle to hole and with each turn into the threads you will turn back one turn to break off the metal shavings (chips) you just created. Never force anything. If it gets tough to turn its time to reverse it and go one turn back to break the chips.

 

[toolman1967]

F size is .2570 1/4 inch is .2500. that is a diff of .0070. Go ahead and use the F size bit and tap the holes. You can go a bit larger on hole size especially with a course tap. You just cant go smaller. Tap it and find out if you have some good looking threads there. If the threads look too shallow, drill the next larger size and tap again.

Great advise from Mike13u on tapping. Use oil to lubricate the tap and turn it 1/2 to 1 turn and back it out to break off the chips made from the tapping process. You will feel them breaking off when you reverse the direction. Go slow and you will get it done.

Good Luck

 

[Kevin54]

Here is a drill and tap chart http://www.shender4.com/thread_chart.htm and another http://www.4hiretek.com/tapdrill.html and another http://www.imperialinc.com/pdf/I_Tap&DieChart.pdf go by it and see what you need. If you broke off a 1/4" bolt but need to go larger, you can drill it out and use a 5/16" bolt. If you need to absolutely use a 1/4" bolt, then you will need to drill it out and Heli-coil it. Here is a chart showing the sizes of drills for a Heli-coil http://www.carbidedepot.com/formulas-tap-helicoil.htm But with a Heli-coil, or Steel Threaded Insert, you will need the proper tap, the insert, and the insert tool.

Use some lube or oil on your tap and if possible, use a two flute tap for extra chip clearance. If the drilling and tapping is going into an area where chips are a major concern, use grease on your tap for lubrication as it will keep most of the chips stuck to the tap instead of falling into the hole.

If unsure of how to do it or feel uncomfortable, go to YouTube and do a search for a video on drilling and tapping a hole. You should come up with quite a few

 

[Vicegrip]

Many hardware stores sell the tap and drill bit as a kit. 1/4-20 is a very common thread size and pitch and you will be able to get them as a properly sized kit. you can get the set and the right bolts at the same time.
Use a lube while running the tap into the metal to reduce the friction and chance of breaking the tap. Even something like spray lube or 3 in 1 oil is better than dry cutting. Turn the tap in until it starts to cut and a 1/4 turn more then stop and reverse the tap a little to break the just made cuttings off. Continue in the same way, turn in a bit and back to break the cuttings off. It helps to back the tap all the way out and blow the tap and hole free of cutting if you are cutting any kind of depth. The cuttings can build up and jam themselves back in the new threads messing up your work. You should get the feel after a bit. The resistance will climb as the cuttings curl and start to get in the way. If you can it would be a good idea to practice on some scrap before working on the intended work.

 

[GeorgiaHybrid]

Your going to have to make the hole a 5/16 hole and use 5/16 fasteners or use Helicoil. If you can afford to make the hole next common size up (5/16), then go to your hardware store and grab one 17/64 drill bit and one 5/16 tap (fine or coarse. hint: if you have never tapped use coarse). You will also need a tap wrench to hold the tap. All that should be less than $20. Tapping is easy. Drill your hole to 17/64. Hold the tap verticle to hole and with each turn into the threads you will turn back one turn to break off the metal shavings (chips) you just created. Never force anything. If it gets tough to turn its time to reverse it and go one turn back to break the chips.

You might want to re-word that just a tad......

 

[Tom Hintz]

I have a quick tutporial on using taps and dies at the link below.

http://www.newmetalworker.com/Howto/usetapdie.html

In the reference section I also have drill/tap charts for the sizes.

 

[porphyre]

Thanks everybody.

Between Walterchang and toolman1967, I think I've got reassurance on what I want to do. As I tried to point out, fastener size doesn't really matter. So I'll use the 1/4" holes I've got now. I'll try the 1/4-20 and see how it goes.

I'll let everyone know how it turns out.

 

[larry_g]

The best way to break a tap is to tap into a hole that is to small. The most common way to break a tap is to give it a bit if side force and snap it off. In addition to most of what is said above make sure your drilled hole is straight, and that you keep the tap straight into the hole. You did not say wheather this is a blind hole or through hole. Blind holes can take a bit more care and if needed different types of taps to make the threads full depth if needed. If your putting on just a plastic cover like in a wheel well that attaches to the sheet metal also consider using a self tapping screw. Can you get a picture for us?

lg
no neat sig line

 

[GeorgiaHybrid]

Thanks everybody.

Between Walterchang and toolman1967, I think I've got reassurance on what I want to do. As I tried to point out, fastener size doesn't really matter. So I'll use the 1/4" holes I've got now. I'll try the 1/4-20 and see how it goes.

I'll let everyone know how it turns out.

If you have 1/4" holes, you will not be able to tap it for 1/4-20 threads. a bolt or stud has a major (outside) diameter (in your case, 1/4" for 1/4-20). You need a drill size that is larger than the minor diameter and smaller than the major diameter. The minor diameter is the dimension from the bottom of the thread on one side of the bolt to the bottom of the thread on the other side.

If you already have 1/4" holes, try drilling with a "J" drill bit (.2770) and tap for a 5/16-18 thread.

Edit: A "J" bit will give you 50% thread and be easier to tap if you are not experienced at it. That will be plenty enough thread for a plastic cover. If you need to attach steel. I would drill it with "F" bit (.2570) to get 75% of the thread but it will be more difficult to cut the threads. Use plenty of tap oil, go slow, stay straight and you will not have a problem. As noted above, back out often to clear the chips and let your tap do the work for you.

 

[nissan_crawler]

Your going to have to make the hole a 5/16 hole and use 5/16 fasteners or use Helicoil. If you can afford to make the hole next common size up (5/16), then go to your hardware store and grab one 17/64 drill bit and one 5/16 tap (fine or coarse. hint: if you have never tapped use coarse). You will also need a tap wrench to hold the tap. All that should be less than $20. Tapping is easy. Drill your hole to 17/64. Hold the tap verticle to hole and with each turn into the threads you will turn back one turn to break off the metal shavings (chips) you just created. Never force anything. If it gets tough to turn its time to reverse it and go one turn back to break the chips.

VERY important part up there...if you don't, the chips will curl up inside the flutes, and lock the tap up in the hole...now you have some real fun coming your way.

Thanks everybody.

Between Walterchang and toolman1967, I think I've got reassurance on what I want to do. As I tried to point out, fastener size doesn't really matter. So I'll use the 1/4" holes I've got now. I'll try the 1/4-20 and see how it goes.

I'll let everyone know how it turns out.

If the hole was for 1/4" bolts, and you already pulled the threads out, it's too late for a 1/4" tap. You need a 5/16" tap, and appropriate size bit as pointed out above by georgiahybrid (NOT a 5/16" bit).

 

[porphyre]

Damn, that was EASY.

Luckily, the set I got had sizes both larger and smaller than 1/4-20, cuz, yeah, that 1/4-20 went right into the hole!

I tapped them out with a 5/16-18. I used some Craftsman branded cutting oil they had on the shelf next to the tap sets. I turned 1/2-3/4 turns or so, then turned back 1/4 turn whenever the effort began to increase. Took like 60-seconds per hole. Really easy. The 5/16-18 bolts I bought fit right in there. There's a little wiggle room, which seems weird to me, but whatever. They snug down nice and tight. Plus they're just holding on some plastic covers.

The second hole was extra fun because the tap handle was interfering with some other parts of the car. I ended up wrapping a layer of electrical tape around the square on the tap, putting it in a 3/8" drive 1/4" 8-point socket, then sticking that on a 3" extension then on a 3/8" slider bar... a bar I randomly got in a CL toolbox and NEVER THOUGHT I'D USE.

Garage Journal tool-hording-itis strikes again!

Thanks guys. Learned a new skill today. Now I won't be so afraid of buggering threads. I can just make new ones.

 

[mike13u]

Good job man!
Now that you know that, you will use it all the time. Its an important shop task.
Make your next major shop purchase a good tap and die set.