There might be threads about this, but it isn’t easy to search for.
I have no current job for which this is an issue. I just had a conversation recently with another DIY’er who is likely more experienced than I and was just wondering…
I’ve long had a reasonably extensive tap and die set, and have often used a tap as a thread chaser. The convo was this other guy telling me how dumb that is, at the very least for torque-critical bolts. (E.g. heads, oil/trans pans, timing covers, and the like). They inevitably remove metal and mess up the tight thread tolerances, was the argument.
I was just like, first of all, I use them greased up to help catch contaminates, and second, I don’t ham-fist it. I know what it feels like when a tap is actually cutting metal, and I know how to lube and be slow and careful. So why go buy a whole other set of something if I already have something that will do the job - if I’m careful.
On a technical level, I know that this “right tool for the job” argument is technically correct. And when I need bottoming (like on head bolts), I’ve just made a make-shift bottoming chaser from an old head bolt. So, I do get the advantages of a true bottoming thread-chaser set. But I’ve gotten by.
But … IDK, maybe I should buy a set of thread chasers and stop using taps. What say you? Especially interested to hear from the pros who do this kind of thing on a daily basis, but obviously all thoughts are welcome.
Thread chasers are necessary to preserve the integrity of threaded components. In fact I insist on replacing whichever component, bolt or nut, when possible when threads are damaged.
Me too, my Dad was a Tool and Die machinist and I inherited a vast array of taps and dies in addition to the ones I have bought over the years. Probably easier to define in terms of pounds than sizes
I have no chasing taps. I have always used my forming taps to clean out or refine existing threads. I fully understand the arguments for chasing taps. However, in my experience, it has never been an issue. You have to be careful and not ham-fisted of course. If I was doing it professionally, then I would invest in chasing taps because it is someone else’s property and I can’t take chances with that.
I’d have no problem carefully using high-quality forming taps and dies. They will only remove metal that is ‘out of spec’ with regard to the desired thread shape. I assume that when you run them into an undamaged thread they meet no resistance and remove no metal.
However, if threads are badly damage and you’re removing a lot of metal with this approach then there is a problem.
Edit - all this only applies to iron or steel threads, not to aluminum castings.
I have never had any issues using my tap & die set to clean threads, true if the threads are already damaged then is a chaser really needed??
I always run a tap in all the engine block holes (head bolt holes, main bearing cap bolts etc etc) just to clean any dirt/crud out… Cleaned a lot of transmission pan rail bolt holes also… I have a few chasers and really never had any luck with them, most of the time I either just use a tap or modified bolt to clean the bolt hole…
I use a tap, too. But I often wish I had a set of stiff, skinny bristle brushes made to run down into old threads so I could clean without also making more junk that falls down to the bottom of the hole. Getting that crap out so the bolt doesn’t bottom out worries me a lot.
I have some cheap tap and die sets. When I was doing engine and trans work for myself, the taps mostly got used to clean the rtv and crud from threaded holes. Blind ones especially. I used my fingers to turn them so I wasn’t cutting just de-crapping. Bolt threads got wire brushed for the same purpose.
If I was doing this professionally, I’d buy thread chasers for quality and to speed things up.
I have a selection of these- some came from barrel cleaning kits. They’re mostly brass bristles which I find less propensity to break with the back and forth bending needed to follow internal threads. I rarely use them and prefer tapping followed by the above.
I’ll have to look into barrel cleaning kits. They would help with smooth passageways and tubes, too. Blasting out holes with air works pretty well - I do it sometimes but there are times when whatever’s in there is pretty stuck. A long skinny screwdriver sometimes scrapes it loose, then the air. After about 50 years messing with machines you learn a couple of workarounds to get a job done.
Limited diy’er experience, takes more time, but I seem to get better results cleaning up a twisted internal thread by making my own tap from the correct size bolt, dremmeling a narrow notch along its length. Of course I start by cleaning the threads the best I can, then tracing the pattern all the way around, cleaning the thread channel with a metal pic. I’ve used a similar technique using a notched nut on external threads. I usually use a small triangle file for the nut-slot. The “improvise your own” tap technique has proved especially helpful on bicycle repairs, where the threads are aluminum & shop taps for those dimensions can be very expensive.
So funny story. But first, I appreciate the replies and knowing that I’m not just an idiot.
But I got to thinking about HF because we had one set up shop in town several years back. Their stuff is generally not great quality, but for certain things it doesn’t matter so much. So I figured if they have a reasonable thread chaser set, I’d pick one up.
I went and searched the site for “thread chaser” and I got a lot of results back - every last one of them was a tap and die set. So now I’m just like “what the heck is the difference anyway?” Presumably thread chasers will all be bottoming, which taps tend not to be. And what? Softer metals without cutting edges, I guess?
The only thread chaser I own is a K-D tools one in 2 spark plug sizes. I have never had to use on spark plug holes but it works great on oxygen sensor holes. Worth all of the dollar I paid for it new in the package off a blanket at an antique car show.
That used to be a great way to buy tools when the national chains were drivingall the small parts stores out of business.
I miss the local stores. A clerk at Twin City auto parts knew I always had Mopars and would see me coming with a part in my hand and have the new one up on the counter before I got to it.
Yes, thread chaser taps tend to be less aggressive and can be used to bottom out versus a thread forming tap that has a taper needed to start new threads.
Additionally, a chaser tap is not as sharp and designed to roll form the threads back into position versus a forming tap that will cut away and remove any interfering material.
They are still hardened tools as the process of reforming threads requires them to be harder than the material they are repairing.
Thinking about this, on nuts and bolts I’m fine using a tap or die to clear threads. Most hardware is replaceable if I mess it up, and the tap set is right there, in the drawer. It’s clearing threads in aluminum castings that worries me.
Your friend is right, using cutting taps weakens the threads. A roll forming tap, sometimes called a chasing tap or thread restoring tap actually strengthens the threads. A cutting tap cuts through the grain of the metal where a roll forming taps distorts the grain, compressing it and making it stronger.
You can rent a roll forming tap and die set from O’Rielly’s free if you return it, about $100 if you don’t.
But sometimes, especially in aluminum, you can’t save the threads. My son and I removed the engine from his 2006 Sentra Spec-V the other day. Yesterday, getting ready to mount the engine on the engine stand, we noticed that the threads at the top of the block for the transmission, the ones that we were going to use to mount the engine with were in bad condition.
Borrowed the thread restoring kit from O’Rielly’s and chased the threads, no luck. They were too far gone, overtorqued from the factory (or dealership). This was one of the cars that was returned to the factory when new (before sale) for a replacement short-block due to bad oil control rings.
