A Long Time Coming
 

My first MtB frame and fork begins in earnest, after about 45 years of thinking about building one. Dual rigid, 650B by 2.5/2,6 wheels. This build will go slowly as there's a lot I still have yet to figure out. For now here's the best photo I have as yet. The blades have been cut down, home made drop outs are brazed in and the top ends of the blades mitered to just touch on the fork's centerline. The plan is to braze the tops together to maintain their alignment during the hole sawing for the steerer miter. Andy
https://cimg4.ibsrv.net/gimg/bikefor...5cee202eae.jpg

Looking good! What kind of brakes are you planning for? A mistake I made on my first fork was having nice far-apart blades for plenty of tyre clearance-- everyone wants huge tyres these days right-- and then finding that V-brake bosses 120mm apart just aren't going to work.

This bike will use disk brakes. I agree with the current trend to fatter tires, I predict skinnier will once again become fashion in 5+ years:) Andy

v brakes are never coming back. Not sure about narrower tires either, the roads aren't fixing themselves.

I like that fixture

I joined the top edges of the blades together (a butt braze) a few days ago, then cut the steerer miter today. I have more details on my Flicker album https://www.flickr.com/photos/731955...57716507964431

The shop is closed this week (we have been doing a week off in mid fall for a few years now, really need it this year!) so more on the fork work will get done soon. But the frame will wait for a computer servicing. I have gained some gremlins, or lost some settings..., recently. I blame the Ruskies and my early voting by mail:) Bike Cad won't open. At least I now have my A-C dimension down to a specific number. Andy
https://cimg4.ibsrv.net/gimg/bikefor...62143913e6.jpg

Always a good idea to make the fork first anyway because then you can measure the axle to crown and if necessary adjust the frame design if it's not exactly what you were shooting for.

On the Flickr you said 0.5mm off. My first unicrown fork was hand-mitred and much further off than that... But forks are quite thick tubing and it's easy to fill a small gap with the welding. Brazing may need a better fit. But it sounds like you won't have an actual gap just very slightly offset blades and a tiny bit more rake.

Usually I get pretty good fits with hand-mitring but unicrown forks are very tricky. For the next one I think I'm going to try and make some kind of fixture and use a hole saw.

Nice job on the fixturing. I have a similar mill and puzzled over how to make that cut for a while. I ended up hand filing them and that was a pain getting them to match.

I don't think I can make that cut on my mill, might have to buy a right angle head

Can you angle the head? I know it's a pain to have to tram it in back to vertical afterward, but if you don't do it often...

Say 45° on the head, and lean the fork jig 45°, or whatever combo gets it to fit. Plus/minus the angle due to fork offset, 8° or whatever that is in your design.

Just idly speculating, I don't know anything about your mill of course.

Mark B

nope, it's a fixed head. Although every time I think about this I realize I could do it in my lathe. A little more setup required.

After doing a number of main frame and stay miters on the mill I'm pretty comfy with this set up. As mentioned it did rake some trial to figure the most solid method. I have to admit that I have not angled the mill head WRT the table yet. I do think it's slightly off as when end milling a top surface i see one side of the cut having slightly more cutting marks then the other side. I wrecked one of my Mit test indicators a few weeks ago (bummer) and had to bring upstairs my other one to reposition the angle vise and the main vice after this miter was done. What was new was using my electronic tach on the mill for the first time. My low speed is about 197rpm (unloaded). That's about 33% faster then the hole saw guide sheet calls for. Andy

Tramming a mill is no fun. Especially one that doesn't rotate.

Last photo for a while. Andy

https://cimg5.ibsrv.net/gimg/bikefor...62c50b1f17.jpg

https://cimg5.ibsrv.net/gimg/bikefor...f165eb47f2.jpg

Paragon drops. Slot angle a tad too much.


https://cimg0.ibsrv.net/gimg/bikefor...fbbebaa09a.jpg

Likely the last time for this brazing jig. It's replacement has been started.

https://cimg1.ibsrv.net/gimg/bikefor...2b48edaffd.jpg

I'm good with this effort. This camera is a bit heavy with the red in the images. Andy

What stays are you using? Any worries about chainring clearance or crank clearance at the pedal end?

The stays are unknown. I've lost the name tag and don't remember who I bought them from (could be a privet purchase even). I do have some concerns about tire and ring clearances but feel confident I can bend as needed. I did a loose mock up and think that the tire clearances will be the bigger job.

I did most of the finish work on them today, here's a shot. Andy

https://cimg9.ibsrv.net/gimg/bikefor...e62e55a3dd.jpg

Do you have any photos of the whole jig? I'm thinking of building something like this.

Here's a shot of an earlier version of this fixture. I wanted something that would allow quick drop out/blade removal during the end's mitering and also fit various tubes. Version 2 has the dropout axle off set from the beam to allow for better torch access to the inside of the blade/dropouts and then had an extendable option added.. Version 3 will space the blades further apart and position the blades more evenly at the plate end.

If you make your own do the layout dimensioning. I wanted the drop out/blade angle to be what a frame/fork sees (about 7-9 degrees) and not have the open ends of the blades/stays touch each other. I also wanted the ability to turn and rotate the fixture while brazing, hence the round jaw held handle. Andy

https://cimg5.ibsrv.net/gimg/bikefor...dc8ed43348.jpg

I'll add this tool and it's replacement to this thread on hand made tools.

Homemade Tools - Bike Forums

I have a lot of small bits and will try posting more there. Meanwhile on this thread's topic I have more components as of today, so I can revisit the mock ups with the proper BB and see if Eric's concerns are my down fall. This will take some time so please stand by:) Andy

To somewhat answer Eric's question better here's the path I have decided on WRT chainstay/tire/ring clearances.

Some backround though for those late to this build. I have wanted to do a MtB frame for myself for decades. This build is carrying all those years of dreams on it... Started a couple of years ago for real. Thought I would want a 3"+ tire, 27.5 as I'm not tall and like a quicker steering bike then some. So i got a Paragon yoke MS2060 - Steel Chainstay Yoke for 3" tire (paragonmachineworks.com) but ended up deciding that 3" tires were just too much and after getting the yoke welded shut moved on from it in the design. After a few months of wrapping my head around the issue decided to scallop out the chain stays and braze in a plate.

I have just finished the torch work today. Had to reduce the stay diameter by about half so went with a fairly thick plate to compensate. I am aiming for about 10mm of side clearance at the tire knob's top edge (it's a fairly square edged profile) and more directly above the center.

I have a lot of plate material removal ahead that will happen in stages soon. The chain ring clearance will have to be visited. The intended crankset has been measured and with no dimpling it will be close. Dimpling should be easy after this step's work though:).

The garage is really cold and I've been delaying the mitering of the TT and DT on the mill. So to the chain stays will likely wait their BB ends miter. Andy
https://cimg6.ibsrv.net/gimg/bikefor...42afdddbca.jpg
https://cimg7.ibsrv.net/gimg/bikefor...271bac12e9.jpg

With that heavy fork I think you need a SA XL drum brake. Bonus is you'll never need to adjust it ever again.
My dyno drum has 26,000 miles with one bearing change. Done 2 tours on my 120 lb tour Rohloff14 bike.

No IGH for this bike. I have 4 of those in my stable already, all SA or SACHS. my new drop bar commuter has the newest a SA RX-RK5 with a Shimano dynamo up front.

This MtB will be a trail bike and hopefully only see pavement when I cross a road. Andy

I thought that it would be a few days before I had the house to myself and I could make the noise that finishing off the chainstays will produce. But the wife changed plans and I had almost 3 hours of "safe" time as she was out running errands. I had done the brazing yesterday. I tacked the loop shaped plate in place on both stays and then cut the stays apart. I hack sawed off as much of the excess plate, then ground the plate's edge down near flush with the stay, first with a rough wheel then a fine one. Next came the 14" ba st erd then the 6" one. I did use my electric belt sander out of motivation from watching Paul Brodie's vids.

This shows the plate tacked in place. Two tacks along both sides (or the top and bottom of the stay), one pair are in view.
https://cimg8.ibsrv.net/gimg/bikefor...3aec79bb90.jpg

Plates brazed up and finishing starts. Top stay has had initial grinding on rough wheel. Bottom one is after the hack saw work. They get hot during the grinding so I alternate between the two stays.
https://cimg5.ibsrv.net/gimg/bikefor...228a61ebd3.jpg

The mock up after finishing the stays. Depending on actual stay end/BB shell placements I should have about 8mm of gap either side, that's what is showing here.
https://cimg7.ibsrv.net/gimg/bikefor...6d2ef3942a.jpg

The finished for now stays. I'll do a bit more detail filing and sanding but not much.
https://cimg4.ibsrv.net/gimg/bikefor...c269c4eeb6.jpg

Next up is the seat tube/BB shell joint. I found out that the shell I planned on using has buggered up threads. I suspect it may have been from a privet sale and part of a bunch of parts. Either way I ordered one (actually two) from Paragon and will wait till they come. I can prep the seat tube by then. Andy

I think that's the neatest and most satisfactory way of dealing with fat tyres that I've seen.

Ti Cycles in Oregon does it in titanium, as a retrofit. Not cheap though!

Disclaimer, I used to work there, when Ti Cycles was in Seattle. Been doing it for years, so I assume it is reliable — I'm assuming I would have heard reports if it wasn't. The chunk he welds in is heavier than the piece he removes, so overall weight goes up a tad but stiffness probably doesn't suffer much. Could theoretically even come out stiffer, depending on how deep the extra clearance goes.

Mark B.