taguy4

I want to convert from the quick release to a recessed seat binder bolt set-up on a Mongoose hybrid bike (which I believe to be about the same bike as the Giant Innova model) I'm working on and have a concern about drilling out the seat cluster for the increased diameter of the tube nut and allen head bolt. Is there usually enough material to do this safely without weakening the seat cluster? The OD of the ears where the bolt goes thru is about 16mm and I would need to enlarge a 6mm clearance hole to at least an 8mm clearance hole. It doesn't seem like much until you start drilling based on my experience enlarging holes on bike frames for one change or the other. I just don't want to ruin a perfectly good frame by doing something ill-advised to it so I thought it'd be good to post the question. The bike has a good quality chromoly tubing frame and fork so I think the seat cluster is probably pretty strong.

Crankycrank

A photo would help but without seeing it you can certainly substitute a regular 6mm nut and bolt in most cases without drilling the holes larger and will be plenty strong enough to clamp the post firmly.

taguy4

I know I can substitute the same size plain 6mm bolt as the 6mm quick release assembly. What I want to do is what my original post said - substitute a recessed allen binder bolt and corresponding tube nut for the 6mm quick release. As I mentioned earlier, the allen bolt and its tube nut would need a 8mm clearance hole since it is larger in diameter, meaning the seat cluster ears (which are 16mm OD) would need to be drilled out a bit. I'm wondering if it's safe to do that without weakening the ears so much that they bend when tightening the binder bolt rather than pulling the top of the seat tube tight around the seat post.

Crankycrank

Yes I understood this but again, a photo would really help so we can get some idea of how sturdy the clamp area is. Drilling would be my last resort if you can sub a bolt that fits the current hole. There are different types of bolts that would still look sleek and not like a hack if you're interested.

taguy4

Here's a picture of the seat post binder as it is now, with clearance holes in the ears for the 6mm quick release mechanism bolt:

Andrew R Stewart 

The photo shows a fairly substantial binder barrel. I would have little concerns in opening it up but I also feel that this is one of those situations where one should ask "why?" before going forward. It seem that you're looking for a detail that the use of the bike doesn't need to exist. Many will say "don't fix a running part". Andy

blamester

You have to judge it yourself.
How much material will be removed and what will be left.
How accurately will you have to drill?
Is there wiggle room if you go a little wrong?
I presume you want a tidier look and that's why you are doing it.
You could try a dome nut on a nice bolt.


​​​​​

Rolla

I don't think anyone can accurately predict the outcome without trying it. While the ears certainly look substantial, they are also currently operating as designed and intended.

Also, to recess the nut and bolt so they sit flush in the frame, wouldn't the hole require a "shelf" for the lip -- and the removal of more material? Would you need to "key" the hole?

taguy4

I'm basically a "if it ain't broke then don't fix it" kind of guy, but if something bothers me enough I'll go ahead and fix it anyway. The quick releasee for the seat binder is big and ugly, and I never know which way to position the lever so it doesn't inadvertently get released and then the seat drops. Also, I did a drop bar conversion to this bike to make it more of a gravel type bike, and having a big ugly quick release lever on the seat binder doesn't really look right on it - it kind of sticks out like a sore thumb.

krakhaus 

Just do it. The worst that will happen is that you drill all the way through and have to use the quick release again. Measure correctly, take your time, you'll be fine.

Geepig

If you want a better look for your bike, I would not recommend using a drill. Instead I would be considering a local machine shop to see if they would mill a recess, because then there would be a good flat step for the bolt head and for the nut. If you drill it then they will have to sit on an angled, and possibly bumpily angled, step.

taguy4

Another option that could be done myself would be a hand reamer. I have some of these and they work really well and give you a lot of control over how much you are enlarging a hole.

Andrew R Stewart 

Don't use a tapered reamer and using a adjustable one will tale a long time to remove 1mm of radius.

There is no mechanical reason to need the bolt's head recessed (as Rolla's photo shows the lug has) so using s counter bore bit isn't needed (and they can be pricy). There's no mechanical reason to need a super smooth barrel ID and that ID really wants to be larger then the bolts by enough to allow the binder to close up around the post and not have the bolt binding up within the barrel.


Just had a thought from your first post. Is the barrel only 16mm long/deep? Have you placed a binder bolt of choice against the binder barrel to see if the two are in agreement lengthwise? How much binder barrel closing is needed to secure the post? What's the barrel's length then? 16mm is pretty short so do your homework. Andy

taguy4

I wasn't planning on recessing the head of the head of the binder bolt because it doesn't look like is was meant to be recessed, although I suppose it could be. The nut end of the binder is slightly splined around it's circumference, so the hole in that ear definitely doesn't have to be super smooth

The total length the bolt has to go thru to each side of the ears is 25mm or so. I have a recessed binder bolt/tube nut that extends to about 30mm (on the inside of each head) before it runs out of threads, so I think the threads would be well engaged when the bolt is tightened down. I don't think I'd want it much longer or the threads might bottom out before it was tightened down enough to hold the seatpost in place.