glockenspieler

I'm building up a Chinese carbon AC024 cyclocross frame with mounts for disc brakes. The threads in the frame (they look like an aluminum sleeve in the frame) appear to be 6mm but when I try to insert the bolt, i get about a 1/4 turn and it stops.

Now, I can't get a pitch gage in there but I don't think there is such thing as a 6mm bolt with anything other than 1.0 pitch. That means that, perhaps, during the build, they did something like run a tapered tap just part of the way in.

I tried to contact the seller (Miracle) and see if they would verify that the threads should be 6mm and 1.0 pitch but no avail.

I'm tempted to use a 6mm bottom tap but I'm also aware that if I'm wrong and screw it up, I'm out about $500.

Thoughts?

miamijim

Try to run the bolt in from the backside. If that doesn't work wait for thread confirmation from the seller. If the seller doesn't respond...run a 1.0 tap through it.

HillRider

Any chance it's threaded M5?

glockenspieler

Actually I swung by the hardware store with the frame and tried a 5mm .8 pitch and the bolt was too small. It really seems like the first thread catches the bolt but then it stops, almost what you'd expect if either the thread pitch was off or they ran a tapered thread way too shallow (although actually I'd expect to get more of a turn from the latter).

I'll wait and see if I can get any response from Miracle Chan... Argh. This is the last thing to do, then cable it, and I'm done. Just want this done!!!

Looigi

Caliper mtg bolts here are 6mm with 1mm pitch, both for post and IS mounts.

bobotech

Are they through holes or blind holes?

glockenspieler

Blind so there won't be any going in the other way.

AnkleWork

Right, because it is impossible to repair damaged threads.

awfulwaffle 

For what it's worth, there are 6mm screws with pitches less than 1.0mm, though the one commonly known as M6 is M6x1.0. See here https://mdmetric.com/tech/M-thead%20600.htm for a list of all available 6mm threads.

Perhaps there's an off chance that your inserts were tapped with the wrong size, but that seems odd given that M6x1.0 is almost always what one sees. Do both mounting holes behave like you described?

Like others have said, try running an M6x1.0 tap through it if you can't get a hold of the manufacturer. If it takes a lot of torque to get the tap to go, I'd back it out, drill the insert to 6mm and try filling the hole with JB weld and then tap that to M6x1.0. That or a Helicoil.

FBinNY 

Buy a bottoming tap, and extend the thread if there's room. Dip the tap in kerosene or spray with WD-40 or similar to keep the aluminum from sticking to the tap.

If there are torque issues, or there's not enough depth, consider drilling through with a 5mm or #8 drill (DO NOT DRILL THROUGH WITH A 6mm DRILL), then tapping with a taper, or plug tap.

cranky old road 

I wonder if you could screw in a softer material (wood dowel? hard wax? plastic?) and then screw it out to see what the threads look like.

leob1

I hope you tried more than one screw, as that may be the problem and not the hole. If you did, sorry for stating the obvious.

rumrunn6

thought this was a hot-or-not thread ... sorry, couldn't resist

gsa103

Are you sure its metric threads? 1/4-20 threading is very hard to tell from M6.

Typically, you can get it to go in about half to a full turn before it jams.

Black wallnut 

1/4-28 is more like m6-1. 1/4-20 is hard to mistake for anything else IMHO.

gsa103

I work in optics. Tables are either M6 or 1/4-20. Wrecked threads are a routine occurrence. Most people just look at the overall size of the screw and don't bother to think about thread pitch.

glockenspieler

Thanks for all the responses, here's a few things:

I did try a range of both metric and english bolts and the only one that really "seemed" like it could fit was the 6mm but I didn't keep track of what I actually tested so perhaps there's a second trip there.

I realized that I hadn't tried the water bottle cage threads so I just did that - same deal. Now in both the bottle cage holes and the brake mounts there was some paint slopped in there so i had to take an old spoke and imitate a dentist and try to pick some of it out of there (gently). Same deal, like I can almost get it started but then it stops before anything close to a full turn.

Just to anticipate one reasonable question - There doesn't appear to be paint in either of them now (it came out in pieces) so I don't paint in the threads is the issue.

This has me back to thinking that there's a different size they are using but who knows? Well, I guess Miracle Chan does (maybe), so I'll give them a couple of days, and in the mean time, I'll take the frame back to the hardware store and be a bit more systematic about the testing.

02Giant 

Chase them with the tap, if they are beyond hope, use a Helicoil.

Kimmo 

The threads are virtually guaranteed to be M6, and since you scraped a bunch of paint out, that's virtually certain to be the cause of the issue. Use a tap to finish cleaning the threads.

Or you can just cut some slots in a M6 bolt with a dremel cut-off wheel, and hey presto - 50c tap.

Neat idea.

glockenspieler

Quick update - Miracle Chan replied to me telling me that there's no need to buy a bolt and that it comes with the disc brakes.

Uhh.... I think there's a bit of a language barrier (their English isn't so good, and my Chinese is even worse).

Anyway, I'm hearing that maybe use a M6 bottom tap, spray with wd40, and tap that. If I somehow manage to screw it up, then there's some hope in using something like Helicoil to still be able to mount the brakes.

Hey, it turns out that you people are pretty helpful, who'd have thought?

hueyhoolihan

well, you DO know the story about the monkey a typewriter and the Declaration of Independence? right?

AnkleWork

The advent of the internet proved that concept false.

rpenmanparker 

Just to assume the supplier is not out to linguistic lunch, what was the source of the bolt you tried? Was it one that came with a set of brakes or just an M6 you had around the house? Do you have the brakes you are going to use? Do the brakes come with bolts? Did you try them?

glockenspieler

No, assume that they are out to linguistic lunch (I'm actually part linguist so I've had those...).

Yes, I started with the bolts that came with the Avid BB7 brakes. Because there was some loctite on it, I also tried a couple of others that I had around that were clean (like left over from removing a bottle cage or two).

FBinNY 

I don't know how new you are to turning wrenches but there is a pronounced difference in feel between a screw of the wrong pitch (thread doesn't match) and running out of thread because the part wasn't tapped full depth.

The former gets progressively harder on a fairly long curve starting almost immediately. Running out of thread will fill 100% normal for a certain number of turns then start getting harder quickly, going from zero resistance to nearly a wall within a turn or two.

In any case, the number of possible thread options is very limited (just about to 1) so unless you found some imperial screw rather than the standard M6 (6x1) you're looking at a badly tapped hole. Time to quit ***** footing, and if you don't trust yourself, pay a pro to assess and solve the problem PDQ.