Thread chasing?? Thread forming??

[HFR_Racer]

I need to chase the threads in my cylinder head for an exhaust stud. Can I do this with a thread forming tap or is a thread chasing tap a completely different animal? Please explain if I shouldn't use a thread forming tap..



I'm having trouble finding thread chasers that are long enough to chase the entire depth.

I can purchase a thread forming taps easily..

Thank you,
HFR_Racer

[cgarr]

Chase are usually like bottoming taps so it should reach the bottom, how deep are you gong? Dont cut any new threads or the stud will be too loose.

[HFR_Racer]

I need to chase at least 1/2" deep. I'd like to chase the whole depth, approximately 3/4" ~ 1".

I can purchase a bottoming type thread forming tap. I simply don't understand if there is a significant different between a thread chaser and a thread forming tap.

Anyone

[cgarr]

Here is a chaser. A tap of any kind will cut and you dont want that. The chaser will only clean out the threads without removing any material.

[brads911sc]

if you are very careful and use very little torque you can use a tap to chase out the loctite from the old threads just be sure its lined up correctly. the better option is to buy the appropriate chaser...

[fanaudical]

When in a pinch, I have sometimes purchased the correct-sized bolt and then cut a couple of grooves in the threads with a cut-off wheel on a Dremel tool. I clean up the threads with a die following the grooving. It's a cheap thread chaser if you can't find one.

[euro911sc]

Originally Posted by fanaudical

When in a pinch, I have sometimes purchased the correct-sized bolt and then cut a couple of grooves in the threads with a cut-off wheel on a Dremel tool. I clean up the threads with a die following the grooving. It's a cheap thread chaser if you can't find one.

+1 This is what I did to clean out the case stud holes. Used a dilavar stud and cut 4 grooves and chased the threads. Worked like a champ!

[lindy 911]

DO NOT USE A TAP! The tap will cut materials from an already tapped hole and create a loose fit. Ask me how I know. I chased the head stud holes with a tap and my brand new studs were now loose. You need an appropriate thread "chaser" or the willingness to install time-serts when you screw up the hole with a tap.

Lindy

[AlfonsoR]

Originally Posted by lindy 911

DO NOT USE A TAP! The tap will cut materials from an already tapped hole and create a loose fit. Ask me how I know. I chased the head stud holes with a tap and my brand new studs were now loose. You need an appropriate thread "chaser" or the willingness to install time-serts when you screw up the hole with a tap.

Lindy

Lindy,

This has been my experience too, but I was told by someone that it makes a difference whether the tap is a cheap one, which probably does not conform to ASME thread standards, vs. a more expensive one that does. Have you or anyone experienced this??

The solution I would go with is, as Fanaudical suggests, get a replacement bolt and cut some grooves in it. JMHO.

[HFR_Racer]

The description of a thread forming tap indicates that it doesn't make any chips. This type of tap actually looks very similar to a thread chasing tap.

I think I like the idea of using a bolt and cutting a minor groove through the threads to serve as the cleaning action when chasing the hole.

[billybek]

Some will use a well worn bottoming tap to do this job. I have taken the high edges off a tap using the side of the stone on a large bench grinder.
I like the idea of cutting slots in a bolt to do this job.

[lindy 911]

AlfonsoR,

I just went out and checked the taps I have and some are made by Craftsman with an ASME stamp on them. Who knows who the actual manufacturer is as lots of companies make things for Sears. I would assume that since there is an ASME stamp on them they would be made to that standard.

I also get some taps from a local machinist supply house and, although I can't find a manufacturers I.D., they do have ASME stamped next to the size mark. I really don't know why you could tap a hole with a certain tap and then not be able to go back into that hole with the same tap and get the same results; it's a mystery. All I can say for sure is that a threading tap will open up the threads and will result in a loose fit.

I'm going to ask Arron Burnham why this is and get back to you all.

Lindy

[Canuck_Targa]

Be careful with the terminology, the original poster is correct in asking if a thread forming tap and a thread chasing tap are different and they are. Regular machine taps cut the threads (as we all know) where as a thread forming tap does no cutting and displaces the material to form the threads. I don't suggest that you use a thread forming tap to chase threads in a hole, the reason being if you are cleaning out crud or loctite or any other debris in the threads it will tend to try to displace it into the threads which can actually loosen the fit.

The thread chaser as shown by cgarr is made to clean the hole with no cutting edge like a tap. This is no different than as some have suggested cutting a groove in a bolt with a dremel or die grinder and running that down, works exactly the same and is way cheaper.

Running a tap into an existing (old) thread hole is dependent on the condition of the existing threads, if they are worn or deformed from torquing, the tap will re-cut the "true" thread and it will normally feel too loose after that. Not recommended on older worn out threads.

As far as quality, I have used everything from the most expensive to the cheapest and really the only difference is the quality of the steel used, the quality ones hold their edge much better which translates to better cutting and better threads. The cheap ones chip the cutting edge then bind and break much easier.

Sorry for rambling, I was a Machinist then a Tool and Die maker for almost 20 years and have tapped about 10,000 holes in my time, so I have seen a hole or two.