Another jig thread

[indrek]

Hi all. New member (old time follower) trying to build a first proper jig. This is where I am right now:

frame_jig.jpg

The main frame is from 80x160 extrusion and behind the seat tube, there is another one 40x160 that I'm planning on fixing permanently (will mill out a slot in 80x160 to make the 40x160 flush). Blue plates are 20mm aluminum. Rear axle will move horizontally, BB will move vertically (plus seat tube angle) and head tube will move horizontally, vertically plus angle. I looked at 44Bikes jig and some other custom ones but for some reason I really wanted to have the front axle present, so that at any point of time I could check the wheelbase and be sure the axles are aligned. The conical inserts and other details requiring turning are in the making atm. Next step will be milling the 20mm plates. But before I do that I'd like to get some advice on the seat and head tube assembly. I could make the jig the other way around meaning the head tube plate is fixed and BB and rear axle are horizontally adjustable, or fix the BB and make the rear axle vertically adjustable... I'm just wondering what would be the most rigid option. Making the head tube fixture the most rigid one seems obvious, but I am kind of liking the current version. The seat tube beam and head tube beam are 40x40 extrusions right now, fixed around an axle from the bottom and then clamped via the red blocks. Am I over thinking the rigidness or should I change the design before I start milling the aluminum plates...

Thanks!

This is how I built my first frame, so having big hopes for the next one:)

IMG_20140614_175637.jpg

[Andrew R Stewart]

Hi all. New member (old time follower) trying to build a first proper jig. This is where I am right now:

frame_jig.jpg

The main frame is from 80x160 extrusion and behind the seat tube, there is another one 40x160 that I'm planning on fixing permanently (will mill out a slot in 80x160 to make the 40x160 flush). Blue plates are 20mm aluminum. Rear axle will move horizontally, BB will move vertically (plus seat tube angle) and head tube will move horizontally, vertically plus angle. I looked at 44Bikes jig and some other custom ones but for some reason I really wanted to have the front axle present, so that at any point of time I could check the wheelbase and be sure the axles are aligned. The conical inserts and other details requiring turning are in the making atm. Next step will be milling the 20mm plates. But before I do that I'd like to get some advice on the seat and head tube assembly. I could make the jig the other way around meaning the head tube plate is fixed and BB and rear axle are horizontally adjustable, or fix the BB and make the rear axle vertically adjustable... I'm just wondering what would be the most rigid option. Making the head tube fixture the most rigid one seems obvious, but I am kind of liking the current version. The seat tube beam and head tube beam are 40x40 extrusions right now, fixed around an axle from the bottom and then clamped via the red blocks. Am I over thinking the rigidness or should I change the design before I start milling the aluminum plates...

Thanks!

This is how I built my first frame, so having big hopes for the next one:)

IMG_20140614_175637.jpg

A few thoughts. Why mill out the spine to have the two uprights sit flush? I see no advantage and serious loss of spine stiffness. Why do you feel that checking the wheelbase is so important? Many feel it is a resultant, not a given. Last don't trust any jig to be straight, that's what an alignment surface is for. Andy.

[adarn]

It looks like you have come up with a cool fixture. I would think a lot about your process and how that would effect what you want to build. I think what you have drawn would be plenty stiff, but a fixed HT angle would probably be stiffer - plenty of fixtures have been built with a fixed HT angle. I think the most important area to make super rigid is your axle assembly.

One more thing, if you just mill a slot in your uprights you can eliminate the red parts in your drawing and it will pull the uprights against the plates making things more square IMO.

Good luck!

[Jonathan]

I like the fixture you have. I could totally build a straight bike with that. Sure, it's not production oriented but its clever. With the saved money you could build a few frames or do a lot of practice in making straight frames. Of course, if the hobby for you includes machining stuff and making tools, then have at it.

[dsaul]

The best improvement I made to my jig has been to make the head tube adjustments (angle, horizontal and vertical) independent of each other, so moving one has no effect the other two. The plate slides up and down on the extrusion for the vertical adjustment.
14578032983_c3dcaf6412_z.jpg
I have the angle adjustment rotate around a point that stays aligned with the bottom of the head tube. If you rotate around another point, you are moving the head tube forward or back and up and down with each angle change.
14557084662_83507d0d76_z.jpg
The horizontal adjustment is done by sliding the plate on the rear of the extrusion. The plate I'm using is obviously not ideal and it will get replaced someday with something that spans the whole spine. This is what was laying around when the idea struck me and it works, so I haven't replaced it yet.
14557085142_6c742ba5ab_z.jpg

I understand your desire to have the front axle and I had one on the first iteration of this jig, but its really not necessary. I just take the x and y measurements from Rattlecad and set the bottom of the head tube where it needs to be.

[Rody]

Indrek,

As you asked, here are my thoughts in no particular organized fashion.

A fixture should be designed around a fixed point. In the case of a bicycle frame, the best datum to use is the bottom bracket. From this point, all other elements can easily be determined. If you create a fixed bb, you can then realize the actual axle points of the fixture, setting up the drop, front center and ultimate wheelbase. Create a rear axle piece that allows for vertical and horizontal travel to create length and drop. Create a removable indicator for the front axle that sets drop and offset, to help you visualize the front axle point and confirm head tube measurements. Though not necessary, it is nice for confirmation that the holistic package is set up correctly.

If you want stiffness and accuracy, stay away from extruded aluminum. This material is commonly used because it is easy to acquire, is fairly inexpensive, and can be cobbled together into a finished product without much effort. It is the use of inferior materials such as this that lead to the presumption Andrew expressed, that a fixture cannot be trusted to be straight.

As you've experienced, a bicycle does not need fancy tools to find a finished form. Create and build to the level that makes you happy.

cheers,

rody

[indrek]

Thank you all for great feedback. I see some valid points there... Regarding the extrusion, I totally understand that they are not the most perfect things to build a sturdy jig, but for the same reasons stated above (cost, availability and ease of use) I will be using them. I'm not sold on the "BB is the best point to remain fixed" theory though. Correct me if I'm wrong, but wouldn't the logic be in the lines of less adjustability / moving options per point (rear axle, BB, head tube) the sturdier the fixture?

Anyway, before I start machining anything else, I got back to drawing board (better spend the time now in the design not redoing things once finished:) and came up with these options:

options.jpg

Currently what I have is the option 1. From these 5 options the ones that seem "good" are the 1st and 3rd. I think the point dsaul made about the independent head tube fixture is quite important so 2nd and 4th will not work on this principle. Is there anything else I'm missing or is there a 6th and better option?

[Rody]

Correct me if I'm wrong, but wouldn't the logic be in the lines of less adjustability / moving options per point (rear axle, BB, head tube) the sturdier the fixture?

Ok, you are wrong.

The material the fixture is constructed of and the accuracy of the machining plays a much greater roll, but as you've already stated that you are abandoning those parameters, the point is moot.

r

[indrek]

So basically if I'll be using the extruded al profiles, then it doesn't matter that much what option I'll choose... whatever works for me then... the accuracy of machining isn't a problem for me, I can go as low as 0.001mm if really needed...

[emanuel]

I'm selling one of my jigs, new one on the way. I'll put something up on classifieds, shortly.

[Rody]

Indrek,

Regardless of the material you choose for your fixture, what should drive the design is the methodology you feel most comfortable with using for set up. It should complement your process and seem intuitive, allowing you to quickly and efficiently set it each time.

Whether using a CAD drawing, something scribbled on a napkin, or shooting from the hip, the process of set up should flow with each setting easily double checked against another for accuracy.

Take some time and make out a number of different frame designs using differing wheel sizes and then visualize the steps you will take to set up the fixture for each one, making notes and then ask these questions:

Is the set up the same each time?

Will the fixture's physical parameters accommodate the range of designs?

Does the design of the fixture compliment your fabrication process; ie...there are not structures impeding your ability to place all frame members and join them.

Does the fixture allow for movement or rotation to allow access to difficult to reach areas?

Does the fixture allow for accurate repeatability?

This should help you flush out the design parameters and determine the ultimate form the piece will take.

I've been through a number of re-designs in my career and can tell you this for sure...you will learn more about bicycle design through the process of thinking through and fabricating your own fixture than sweating together tubes will ever teach you in the same time period.

Best of luck,

Rody

[Will Neide]

...you will learn more about bicycle design through the process of thinking through and fabricating your own fixture than sweating together tubes will ever teach you in the same time period...

^
A whole lot of this.

I dont use the design in question, but I did learn a ton in making my own. I'm on a beam jig, although much different than your originial in your OP, so things are little different for me.

Good luck and have fun!

[MrkiMedo]

Indrek,

Regardless of the material you choose for your fixture, what should drive the design is the methodology you feel most comfortable with using for set up. It should complement your process and seem intuitive, allowing you to quickly and efficiently set it each time.

Whether using a CAD drawing, something scribbled on a napkin, or shooting from the hip, the process of set up should flow with each setting easily double checked against another for accuracy.

Take some time and make out a number of different frame designs using differing wheel sizes and then visualize the steps you will take to set up the fixture for each one, making notes and then ask these questions:

Is the set up the same each time?

Will the fixture's physical parameters accommodate the range of designs?

Does the design of the fixture compliment your fabrication process; ie...there are not structures impeding your ability to place all frame members and join them.

Does the fixture allow for movement or rotation to allow access to difficult to reach areas?

Does the fixture allow for accurate repeatability?

This should help you flush out the design parameters and determine the ultimate form the piece will take.

I've been through a number of re-designs in my career and can tell you this for sure...you will learn more about bicycle design through the process of thinking through and fabricating your own fixture than sweating together tubes will ever teach you in the same time period.

Best of luck,

Rody

Maybe this is time when I can abuse this thread and chime in with few rookie jig questions of mine?

1) How precise it needs to be? (maybe this can be answered only in terms of precision of expected results, that is fine)
2) is it necessary for it to withstand large forces and temperatures? When I started thinking about what fixture I am going to need, I thought it is, but if fixture is used only to pin or tack, and rest of the process is carried in bike stand, well maybe this is less important, and some other aspects more?

Let us assume the fixture needs to allow both lugged and fillet based bikes.

[Andrew R Stewart]

Davorin- I'm no pro builder but I have used quite a few jigs over the years.

I'd make the jig as precise as i could without breaking the bank. But it's being flexible for different tube shapes and diameters is more important, IMO. The angles and c-c dimensions are important to be spot on too. Your flat surface and your builsequencece is what will make the frame straight, not the jig.

The jig needs to be stout enough to withstand the weight of the frame during the tacking step. I would not plan of doing the complete brazing while the frame is mounted in the jig. Access to the joints will be hampered and you'll be swing around a vawkwardward and heavy mass compared to just the frame. This is even more the case when fillet brazing.

The ease of set up has been mentioned. This included being able to install and remove each tube without disturbing the jig's geometry, or being able to re establish the settings easilaccuratelyritely. Through rod held head tubes are a pain to work with, as an example. Andy.

[Andrew R Stewart]

This forum has the worst spell check!

"builsequencece" is build sequence

"vawkwardward" is very awkward

"easilaccuratelyritely" is easily and accurately

Andy.

[Todd Mosley]

Here is a 6th option that I built. I based the design around Anvil's adjustability. The bottom bracket is fixed and everything else adjusts independently - reach, stack, head & seat tube angle, chain stay length, and bottom bracket drop. It is accurate "enough".

[Rody]

1) How precise it needs to be? (maybe this can be answered only in terms of precision of expected results, that is fine)
2) is it necessary for it to withstand large forces and temperatures? When I started thinking about what fixture I am going to need, I thought it is, but if fixture is used only to pin or tack, and rest of the process is carried in bike stand, well maybe this is less important, and some other aspects more?

Davorin,

A fixture should be the most accurate tool you are able to procure/produce. There are so many variables in fabrication (think coping, heat input, material stresses) that accumulate during the progression of the build that having an accurate baseline to begin with is imperative.

Fixture stability, especially for beginners, is extremely important during joining, as heat/flame control and access to joints is often not as precise as one would like, so the ability of the fixture to absorb the stray flame or overheating without warping or flexing is crucial.

rody

[back40]

I've taken a slightly different approach. I do all my frame design in 3D CAD (Solidworks). I have a model of the jig I constructed in CAD as well. I "mate" or fit the frame CAD to the jig model with a few simple steps and generate a jig setup drawing. Few if any of the setup dimensions are directly related to standard frame geometry measurements.
The jig design is based on a fixed BB shell. The head tube is always perpendicular to the base frame. The seat tube angle is set as the 90 +/- difference between the head and seat tube angle. The top tube and down tube are free to locate based on their mitered ends rather than being forced into position by the jig holding them. The construction is 1"x2" solid aluminum with 0.05" fly cut off both wide faces for flatness.
Results are such that glued carbon frames are more than acceptably straight right out of the jig. If I build another jig there are a lot of things to improve but I've found the overall layout and setup pretty easy to use.

jig model.jpg

jig drawing.jpg

Jig Setup.jpg

Jig 1.jpg

[Rody]

Glen,

Interesting and effective approach...with more integration of 3D modeling in bicycles, this is a natural progression for computer savvy builders.

rody

[Mike Mcdermid]

I've taken a slightly different approach. I do all my frame design in 3D CAD (Solidworks). I have a model of the jig I constructed in CAD as well. I "mate" or fit the frame CAD to the jig model with a few simple steps and generate a jig setup drawing. Few if any of the setup dimensions are directly related to standard frame geometry measurements.
The jig design is based on a fixed BB shell. The head tube is always perpendicular to the base frame. The seat tube angle is set as the 90 +/- difference between the head and seat tube angle. The top tube and down tube are free to locate based on their mitered ends rather than being forced into position by the jig holding them. The construction is 1"x2" solid aluminum with 0.05" fly cut off both wide faces for flatness.
Results are such that glued carbon frames are more than acceptably straight right out of the jig. If I build another jig there are a lot of things to improve but I've found the overall layout and setup pretty easy to use.

jig model.jpg

jig drawing.jpg

Jig Setup.jpg

Jig 1.jpg

you know what when we designed ours that concept of 90 degrees was included ,seemed the easiest way of doing it ,framebuilders new to it however like to have the frame sat in a position that looks like a frame ,which often compromises lengths of parts ,offsets , materials etc but makes the number on the drawing the number they want to work towe had a concept that used a DRO similar to a milling machine on the axes so you just slid the positioning parts based on two right angled triangles in x or y and then angle KISS ,i dont understand why no one has done a modern take on the traditional sizing board type