A modular frame building system

[incepi]

This is my prototype frame fixture. It's not a fixture in the traditional sense. It's more of a modular system for holding tubes so that the centres are in the same plane. The hourglass shapes are essentially cylindrical v blocks. They can hold tubes with diameters ranging from 1"OD to 2"OD. Any shape of tube can be held in place above a working surface. Not just straight round tubes, but also tapered or bi oval shapes. It can also handle curved or bent tubes. Odd shaped tubes such as those created by hydroforming or carbon fiber molding can be held as well.

The system is for front triangles only. A rear triangle system is in development. The parts shown are 73mm in height, so that tubes are automatically centered on a 73mm bottom bracket shell. A spacer is needed for 68mm bottom bracket shells.

With five 'hourglass' shaped parts(and some simple blocks to assist in constraining the tubes) you will be able to make a front triangle of any shape or size, using almost any type of round or oval tube. I couldn't find a less expensive, more flexible system. So I invented one!

IMG_0722.JPG
IMG_0723.JPG
IMG_0718.JPG
IMG_0728.JPG

[Zimmermanbicycle]

cool,what if one side was set for 68mm BB?
-Eric

[devlin]

You could loose the extra blocks and just extra strong rubber bands to hold the tubes to the vertical v blocks. I really like the lateral thinking here.

[incepi]

You could loose the extra blocks and just extra strong rubber bands to hold the tubes to the vertical v blocks. I really like the lateral thinking here.

I was considering something heat resistant like band clamps or twisted wire.

[Chauncey Matthews]

BB shells are usually wider than 68/73 and lugged sheels can sometimes be wider or narrower than than that. you'd be better off keeping the shell above he table and attaching it to the st before you set things up in the cones.

[incepi]

BB shells are usually wider than 68/73 and lugged shells can sometimes be wider or narrower than than that. you'd be better off keeping the shell above he table and attaching it to the st before you set things up in the cones.

Simple shims could be used to accommodate bottom brackets that are not exactly 68mm or 73mm. Or the shells can be faced on one side. The tapered cylinders can also be shimmed. It might be necessary to do so anyway if the reference plane is not flat enough.

I'll miter some inexpensive 4130 tubes and test the system. At least I now have a reasonably precise frame jig to begin with, and it cost me next to nothing.

[incepi]

cool,what if one side was set for 68mm BB?
-Eric

That's an interesting option. For 68mm shells I will just use a 2.5mm spacer to raise the centre of the shell. I like your idea though.

[crumpton]

So I invented one!

how long have you been around this gig? i saw my first glimpse of a lugged frames coming together on V blocks atop surface a surface plate in about '81. tubular structures have come together that way for as long as tubular structures have been put together.

i mean you have done nice work here but invent is a stretch.

[e-RICHIE]

how long have you been around this gig? i saw my first glimpse of a lugged frames coming together on V blocks atop surface a surface plate in about '81. tubular structures have come together that way for as long as tubular structures have been put together.

i mean you have done nice work here but invent is a stretch.

Jan Legrand (Presto Bicycles in Hollland) was doing this in the early 1970s when he made the Raleigh Team frames under contract.

[incepi]

how long have you been around this gig? i saw my first glimpse of a lugged frames coming together on V blocks atop surface a surface plate in about '81. tubular structures have come together that way for as long as tubular structures have been put together.

i mean you have done nice work here but invent is a stretch.

I am already aware of several designs that use v blocks or clamps to elevate tubes above a flat surface. I don't claim to invent that concept. What is original about my idea is that the tapered cylinders can accommodate a variety of sizes, curvatures, and profiles(including tapered shapes), and that one cylinder can position two tubes simultaneously from different angles. I have not seen that before.

[e-RICHIE]

I am already aware of several designs that use v blocks or clamps to elevate tubes above a flat surface. I don't claim to invent that concept. What is original about my idea is that the tapered cylinders can accommodate a variety of sizes, curvatures, and profiles(including tapered shapes), and that one cylinder can position two tubes simultaneously from different angles. I have not seen that before.

It's a nice effort and I look forward to seeing its evolution. From experience I will suggest that the tube centerlines are more important. Keying in on surfaces, or O.D.s, or tube shapes, can compound all the linearity errors you'll find in every pipe you pick up. In short, they're not straight. Locking down a series of pipes (that aren't straight) will introduce stresses at all the interference fits and junctures. To my mind, again writing from experience, it's unavoidable.

[incepi]

It's a nice effort and I look forward to seeing its evolution. From experience I will suggest that the tube centerlines are more important. Keying in on surfaces, or O.D.s, or tube shapes, can compound all the linearity errors you'll find in every pipe you pick up. In short, they're not straight. Locking down a series of pipes (that aren't straight) will introduce stresses at all the interference fits and junctures. To my mind, again writing from experience, it's unavoidable.

It's not difficult to fixture the head tube centerlines with cones. The same is true for the top of the seat tube.

The other tubes usually have to be held by the outside. As theoretically imperfect as that method may be, it is a practical(and commonly used) solution. If they are not held by the outside, then they are dependent on perfect miters to line up their centers with the centers of the adjacent tubes. So it's a trade off between imperfect tubes positioned("locked down") by their imperfect exterior geometry, or imperfect tubes positioned by their imperfect miters.

Whatcha gonna do?

[e-RICHIE]

It's not difficult to fixture the head tube centerlines with cones. The same is true for the top of the seat tube.

The other tubes usually have to be held by the outside. As theoretically imperfect as that method may be, it is a practical(and commonly used) solution. If they are not held by the outside, then they are dependent on perfect miters to line up their centers with the centers of the adjacent tubes. So it's a trade off between imperfect tubes positioned("locked down") by their imperfect exterior geometry, or imperfect tubes positioned by their imperfect miters.

Whatcha gonna do?

What to do?
Don't hold them at all. With the head tube and seat tube in place, you don't need to hold the other two. The miters locate them against the areas they're mated to. The path they take from one end to the other doesn't really matter as long as the biomechanical axis (seat tube) and the steering axis (head tube) are secure and in plane - and placed there without stress or force.

[edoz]

I am already aware of several designs that use v blocks or clamps to elevate tubes above a flat surface. I don't claim to invent that concept. What is original about my idea is that the tapered cylinders can accommodate a variety of sizes, curvatures, and profiles(including tapered shapes), and that one cylinder can position two tubes simultaneously from different angles. I have not seen that before.

I made one of those to hold the seat tube in my fixture. I don't remember where I got the idea, but I poached it from somewhere else. Good effort, though. It's a nice, simple package that should handle just about anything you want to put in it. Are you going to do smaller cylinders on a vertical rod for chain and seat stays?

[incepi]

I made one of those to hold the seat tube in my fixture. I don't remember where I got the idea, but I poached it from somewhere else. Good effort, though. It's a nice, simple package that should handle just about anything you want to put in it. Are you going to do smaller cylinders on a vertical rod for chain and seat stays?

I have not decided on the design of the rear triangle system. I may use small cylinders, or go with something more traditional.

I was considering something similar to the system used by Rock Lobster for the rear triangle. Instead of attaching to the seat tube, I would use the bottom bracket.

The method is described here. I like the economy and simplicity of it.
what's up in Santa Cruz: Here's how I use my rear triangle jig

[incepi]

All of the suggestions so far are very helpful, but I will test the system as is just to get a frame built. After that I will consider modifications based on experience. I just want to get something built. I enjoy designing to perfection. Sometimes though you just have to make do with what you have. I still have to develop the rear triangle fixture. The challenge will be to make it as simple as the front triangle fixture without sacrificing precision and flexibility.

[David Tollefson]

...After that I will consider modifications based on experience...

The irony is strong with this one.

[Will Neide]

Look into the Sadoff method for rear triangles.

what's up in Santa Cruz: Here's how I use my rear triangle jig

[incepi]

The irony is strong with this one.

No comment.

[incepi]

A little update on the tube holding system. Nothing of substance. Just an excuse to show red anodized parts.

FullSizeRender (8).jpg