BruceMetras

M5 is the size of the bolt .. .8mm is the thread pitch.. .50mm would be finer (more threads /inch) 1.25mm would be coarser (less threads/inch) .. definitely not ok to try to force 6mm bolts... you should have someone with some experience look at your project..

budgee

No, I did not use force to use the 6mm bolts. It is the size as per the Tern frame mounting for the front block.
The Brompton frame mount is using 5 mm bolts. So the Brompton front block needed to be drilled bigger as well as wider apart. The distance between the holes is further apart for the Tern compared to Brompton.
And I did not use a power drill. That would be quite difficult. I used something finer, a rotary tool from Black & Decker. It's something similar to the Dremel tool. And I had the long extension cable to allow fine drilling movements much like what a dentist uses.
Please do plan in advance what you would like to do as the Brompton block is made of plastic and once too much material is removed, it will be unusable. Do go slow with your project. Good luck!

Winfried

Thanks for the infos.

I'm not sure I understand why you used 6mm bolts if the holes on the frame on the Tern are 5mm, though.

While the bolts are 5mm, the "holes" (don't know the technical term) in Tern's luggage truss appear to be 6mm.



But if both Brompton and Tern use 5mm bolts, how come the Brompton luggage block uses 5mm holes while the Tern luggage block uses 6mm holes, requiring the use of a rotary tool to widen them on the Brompton block to be able to attach it to the Tern?

Confused, but curious :-)

budgee

To set things clear.
1. The Brompton Front Block holes and the frame holes and the bolts are designed for the 5mm bolts.
2. The Tern Front Truss holes and the frame holes and the bolts are designed for the 6mm bolts.
3. In addition, the distance between the holes on the Brompton and on the Tern are of different length.
4. The frame backing plate on the Brompton is smaller and narrower than the frame backing plate on the Tern.
There lies the difficult part of making the two different designs match up.

In the photo below, the smaller bolts are the original Brompton front block 5mm bolts. The longer and larger 6mm bolts I purchased separately will fit the Tern nicely.



Hope this helps.

fietsbob

5mm nominal, diameter threads per MM is 0.8 ; Six by 1, is is a bit larger diameter and the thread frequency a bit coarser and comes out evenly to 1.0 TPMM

NO (I had a father who was a skilled Machinist , so that is why I'm not supporting Bodging it when doing it right is not that much more difficult)

But you can have a shop with a thread cutting Tap enlarge the hole and make a new set of threads ..

But I expect you must Remove the Fork.. in order to get the tapered tap to cut clean thread in fully in order to actually get a well threaded head tube fitting.

Winfried

Thanks much for the precisions.

To make [strike]matters worse[/strike] things more interesting, the inside of the Brompton luggage block must be carved to fit the Tern frame backing plate:


I'll go to a fablab on Saturday to have access to the right tools.

ThorUSA

I doubt that they fit, as the Tern and Dahon have their headtube in one piece... meaning the black sits on the outside of the tube. Too long screws would just bottom out and would not hold anything ... or worse would do damage to the headtube inside.

Tern and Dahon have the same "standard" in lieu of better words ... those measurements started out from Basil and Rixen a Kaul ( Klickfix)
for a short time there were also a 3 hole attachment ... which had one hole close to the outside holes if I remember right ...

fietsbob

Machining a extension Block held down with the 6mm bolts , Probably of Steel can then have the piece Like Brompton uses as Part of It's face .

to fit the plastic Bag Mount Onto the extension piece with the 5mm screws

A custom fabrication project .. make 100 and they may sell

budgee

Ahah, This project is already underway by our fellow member bike.gang.uk ..
see his post on 3rd Jan in this same thread.. he created an adapter with the same idea.

budgee

After I had installed the Brompton front block and started using the Brompton C bag and Mini O Bag on my Tern, some friends noticed it and asked me to do it for their dahons and terns too.


My Tern verge P18
https://farm8.staticflickr.com/7407/1...9c005c8f_z.jpg

https://farm9.staticflickr.com/8595/1...7382c2e3_z.jpg

https://farm9.staticflickr.com/8673/1...67c6d1a9_z.jpg


Dahon
https://farm9.staticflickr.com/8662/1...0363a454_z.jpg

https://farm8.staticflickr.com/7308/1...c82cf76b_z.jpg

https://farm8.staticflickr.com/7403/1...bd5f815e_z.jpg


Tern Verge X10
https://farm8.staticflickr.com/7458/1...011db9e1_z.jpg


Block with the modification

https://farm8.staticflickr.com/7293/1...06b6884e_z.jpg

https://farm9.staticflickr.com/8618/1...4a541600_z.jpg


The thread of the nuts are drilled smooth so that they act as washers. Either that or buy slightly bigger nuts so that they cannot be screwed on the threads, they have to be loose to enable the tightening of the bolts to the frame up to an adequate torque to withstand the weight of the bags.

https://farm8.staticflickr.com/7296/1...30a0651f_z.jpg


https://farm9.staticflickr.com/8670/1...96a69746_z.jpg

Azreal911

wow i gotta say that's very creative of you, since the terns and and brompton spacing wasn't too far off i guess you where able to do it with some minor modding to the block. and being able to use the brompton bags would just at least open up your choices even more!

good stuff!

Winfried

Thanks much for the infos + pictures. I did a mash-up:


Instead of piling up several nuts, what about carving out the inside of the Brompton block so that it will fit the welded part on the headtube?


I'll wait for bike.gang.uk's adapter and compare the two solutions before possibly modifying my Brompton luggage block.

Hopefully, the part welded on the headtube of Dahon/Tern will be able to carry a T-Bag even when screwing a Brompton luggage block with either of those solutions.

budgee

Yes, you can carve the Block to fit the Tern's welded part on headtube. That will mean that the Block is quite close to the headtube. One thing I found was that the Dahon and the Tern's handle stem post is angled forwards. This may mean that the space between the stem post and the T Bag metal frame is too close and will touch each other.

One advantage of using the bolts that I used, is that I can use even longer bolts to make the Front Block protrude further away from the bike to allow more free space for the handlebars to move freely while I mount a T Bag or C Bag. This is what I found for the Dahon. So if I get longer bolts, I just file down the bolts to the right length and ensure a tight fit without damaging the bike's head tube.. because there is a distance of about 6mm within the welded part for the bolt to screw in before it touches the head tube. You need to file down the bolt to about 4.5 mm (from washer to the end of the bolt) after using the right number of washers in place.

Winfried

Thanks for the feedback.

I don't have a T-Bag yet so can't test it, but on the Verge P20 at least, there's enough room between the handle stem post and the baggage frame:

QFCFA Front carrier frame only, standard | Brompton Bicycle

It's more cables that get in the way, but they can be held closer to the post so they don't interfere.

Winfried

Went by a fablab. According to the person I showed the Brompton block, the material is too hard to be carved with a Dremel drill.

So it looks like the only two viable solutions are either piling two or three nuts (Budgee), or making a custom adapter that would sit between the frame and the Brompton block (bike.gang.uk).

jur

Too hard? That sounds like BS. I would modify the plastic block in a heartbeat.

budgee

Too hard? That is quite soft material against the Dremel drill ... I used a similar tool, Black & Decker rotary tool and I had to take care as the material was being churned out too quickly.

I think he /she just is not keen to do the job, perhaps not much money for the amount of time needed as it needs to be quite precise in the carving out. And if it doesn't fit the Tern, what then? Refund?

For me, I just used my eyes and some rulers as the ones I did were much easier to do.
By the way, the Dremel drill can drill through steel and cut through metal locks.

Winfried

Thanks for the feedback. It wasn't a money issue since it's a free-access fablab; Just incompetence :-)

If carving the Brompton block with a mini-drill is no biggie, why did you choose to keep it intact and insert nuts instead?

budgee

I did this way to allow the block to be further away from the head tube to allow the C Bag to clear the handle post.

The other reason is that I did not want to remove too much of the material as the block is a solid piece of plastic and gets its strength from the thickness of the structure. Putting a 7kg bag onto that block will actually put a lot of stress on the place where the bolts are holding it in place. Especially when the bike goes over a pothole by mistake at speed. A 7kg bag may put a strain on the block at up to 10kg for a split second while the bike slams into the hole and the block will undergo tremendous stress then.

After I modified the block I found that it can still be used in a Brompton with the original 5mm bolts.
Just in case I wanted to sell the Tern and buy a Brompton, I still can take it out to re-use it on a Brompton.

jur

What I would do: Use a file to get rid of the rib at the top and bottom so it could go over the Tern fitting, then with a round small file elongate/enlarge the holes. Maybe only get rid of the bottom rib and enlarge both holed, one maybe elongated a bit. Done.

If you wanted it to be used for both bikes, I would simply have one for each bike.

fietsbob

Klick Fix does have its own Plastic, bag mounted plates , to build your own front bag around.

since they sell to other bag makers they are available separately This is not so true with Ortlieb. They're Integrated with the Bags too Much.

Dont think the O Bag mounts are available anywhere but on the bag itself.

Winfried

I'll probably do that, and see how it fares when hitting a pothole.

BTW, is there a material that I could easily use to take a moult of the inside of the Brompton block and the Tern frame piece?

jur

Make a negative with some clay and pour wax in.

Winfried

Widening the two holes and making them oval was simple enough using a vertical drill.

Before I bother finding a piece of metal as thick, cutting it to size, and piercing two holes… do you guys think the metal plate provided by Brompton is really necessary?

jur

The plate spreads the load to a larger area. So to achieve the same mass holding spec, I would say definitely. Otherwise the plastic would shear off first around the top screw head then the bottom one.

I don't think the thickness is important, as long as it is stronger than the plastic underneath. It could probably be made from aluminium, if it isn't already.