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Discussion Starter · #1 ·
Hello everyone,

I’ve been lurking in this forum for some time now, following the stuck threads, other beginners, etc and now I’m finally going for it! I have access to a nice jig, TIG welder, and have fabricated my own tubing notcher on a metal lathe. I have started making maple tubing blocks, and still haven’t decided if I need V-blocks since I can use the jig to mock up the tubing (I think).
I still need plenty more practice on the thin-metal TIG welding, and the notcher needs dialed in, but in the meantime, I’ve been working on my plans. I’ll post a picture and geometry chart below, along with the tubing I have already purchased. Basically, I’ve designed a 1x10 (no derailleur or chain guide, 32t narrow/wide ring only) hardtail around a 100mm fork (probably Reba) with aggressive geometry that can be ridden hard. I weigh 220# and I want this bike to be strong and reliable, which is why I’m not concerned about weight. I am interested in any feedback you guys have about anything I have posted here, but I do have some specific questions as well:

• Is it possible to notch my stays and TIG weld my dropouts, or is it recommended to braze them on a plate dropout?
• Is this frame ok without ST sleeve? I know it is highly recommended around here, but with a 1.6mm wall thickness on my ST, maybe it’s ok?
• I’d like a little lower standover, would it be safe to drop TT @ ST about 1.5” and add a gusset?
• With the offset ST, do you recommend any gussets at BB region?
• I don’t have a wheel to measure at the moment, and I settled on 29.25” Dia. for the design; is that about right?
• With my setup, is my headtube long enough to be strong (105mm)? About ½” between TT and DT
• Do I need brake support w/ paragon dropouts having the brake mount built into the dropout?

As you can see below, I used the 2d sketch feature in Inventor since BikeCAD wouldn't play nice with my computer, and I’m familiar with the program. So far, so good!
Geometry.JPG
frame sketch2.jpg

My next steps are to 1. Complete a chainstay drawing to make sure I can squeeze everything in there. 2. More TIG practice 3. Finish tubing blocks.

Thank you guys for any feedback! I already bought materials for this, but if there are any glaring errors, I'm happy to return and buy the right stuff where needed.
 

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Nemophilist
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Hey;

Enjoy the dive!

Noob to noob answers to your noob questions;

1) No reason not to TIG as long as you do not plan to build up or fill a lot. Filling with TIG gets things too hot.
2) .063 should be PLENTY thick for a straight joint. In fact, you might drill and tap them in! ;)
3) Mr. Walt always said no more than 2" or so of unsupported length above the TT, if memory serves me correctly. You may have some leeway with that thick tube, but no sense pushing your luck either.
4) Probably not necessary, but it certainly couldn't hurt.
5) For me? No wheel = no build. That's just asking for trouble. I take the dummy approach. Once you've done a few dozen, you can slide through on your vast experience with such stuff.
6) I would ALWAYS make my HT as long as I could. I'm uncut steerer size, so it is never a problem for me.
7) No.
 
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Thanks for pointing out that seat tube, I've never noticed it before. The thick section looks like its 75mm long so and inch and a half would still be to the thick part. Tigging the ends of the stays to fill them in does put a lot of heat in them. Sometimes I use a pulse setting of 30pps and lower the heat and build up the filler, then go over it hotter to blend it in. May just be easier to use silver like fillet pro. Those paragons are stainless so no brass.
cheers
andy walker
 

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Random thoughts!

-.6mm seatstays are not going to be fun to TIG weld if you are not pretty good at TIG in weird angles/tight corners on thin-to-thick. Get some .8mm or even .9mm if you can find them.

-I'd go 38mm on the downtube as Dr. W suggests.

-The 1.6mm seat tube is thick enough to weld directly to BUT keep in mind that if you are throwing lots of heat at it it'll distort a bit more than a sleeved joint will - meaning more work to ream back to vaguely round to get a post in.

-42cm chainstays on a 29er are not super hard to do but you are going to be cutting things very close on clearance so mock up your chainstay assembly with your actual cranks and ring in hand to make sure you've got something that will work.

-Yes, you can lower the toptube and add in a brace. Be aware that unless you do it carefully you may end up pulling the seat tube forward at the top and have odd problems with the effective angle/saddle positioning.

-You do not need any extra bracing for the brake side stays with a dropout-integrated disc mount.

-Yes, you can slot and TIG, assuming you are decent with the torch. I do it on basically all my frames.

Keep us updated!

-Walt
 

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The cat's name is jake
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A 1.6mm thick Seat tube sounds AWFULLY thick to me. I'm not sure why you'd want it that thick, to be honest. Are you relying on the material thickness to maintain roundness after welding? I'd consider alternately making a heatsink instead, and then honing the bore to fit your seatpost and using a thinner seat tube. With TIG welding, differences in base metal thickness cause as much trouble as anything. Thin to thin is easy, but thin to thick can be more challenging in many cases (though not all), and can cause problems after the fact.

I'd also consider giving yourself a little more extension on the HT, from the intersection of your DT especially, but your TT as well. Welding the DT and TT will really want to distort the HT when the tubes intersect close to the edges. This is still the case for me, even though I've welded 2-4+ frames a day for many years.

I second John's (TrailMaker) sentiment about the wheel. It is important to be able to reference the wheel for several reasons. One is simply for proper placement of bends and bridges, but it also is very helpful for alignment purposes. You will want the wheel centered with respect to the seat tube, but also balanced between the seat and chainstays. It is very handy for this, as you can use a caliper to measure between the rim and the stays, and sight down the back of the wheel up through the seat tube and head tube. Furthermore, it would be good to either have the cranks, or know the chainline and where the end of the crankarms sit relative to something you can reference, such as the edge of the BB shell. Sometimes, the crank may sit such that your heel will clip the chainstay if it sits out further than necessary. Having the crank can help you determine whether there is sufficient room for heel clearance (and of course ring clearance).

That is a nice looking design otherwise, and you appear to be well on the way to making an excellent bike. Good work!
 

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Discussion Starter · #7 ·
Thanks for the replies everyone! As far as the seattube, I thought it sounded pretty thick as well, but wouldn't a sleeve present essentially the same problems (thick to thin)?
On the headtube, I think I am going to go longer, and further from the ends to prevent warpage. Unfortunately, when I just throw a 130mm HT into my drawing, my reach and stack get pretty whacked out, so I need to do some thinking geometry-wise there.

I'll make sure to get my hands on wheels and cranks before going too much further thanks to people's advice here.

I'm totally up for making the bike stronger by adding a bigger DT, but I have run into another problem: when I add a straight 35mm DT, it looks like the fork crowns may not clear. I can't find a bent 35mm DT that is in stock anywhere. Is there a source for any CAD files on common fork crowns? Seems like getting my hands on the fork sooner than later wouldn't hurt, either.
 

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Discussion Starter · #8 ·
I'd probably lean towards at least a 38.1 downtube. Are you designing around the fork sagged?
Looking at working out the DT upgrade. I am not designing around the fork sagged, but I have been keeping it in mind. Do most companies list their static geometries? I have been using bikes that I like to inform my design, but can see the value in designing around sag as well. Do most of you guys do that for front suspension hardtails?
 

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Discussion Starter · #9 ·
Random thoughts!

-.6mm seatstays are not going to be fun to TIG weld if you are not pretty good at TIG in weird angles/tight corners on thin-to-thick. Get some .8mm or even .9mm if you can find them.

-I'd go 38mm on the downtube as Dr. W suggests.

-The 1.6mm seat tube is thick enough to weld directly to BUT keep in mind that if you are throwing lots of heat at it it'll distort a bit more than a sleeved joint will - meaning more work to ream back to vaguely round to get a post in.

-42cm chainstays on a 29er are not super hard to do but you are going to be cutting things very close on clearance so mock up your chainstay assembly with your actual cranks and ring in hand to make sure you've got something that will work.

-Yes, you can lower the toptube and add in a brace. Be aware that unless you do it carefully you may end up pulling the seat tube forward at the top and have odd problems with the effective angle/saddle positioning.

-You do not need any extra bracing for the brake side stays with a dropout-integrated disc mount.

-Yes, you can slot and TIG, assuming you are decent with the torch. I do it on basically all my frames.

Keep us updated!

-Walt
I'm going to look into thicker stays. Thanks for the suggestion, I can imagine that would be a challenge, especially after my TIG practice session yesterday!

I think I'm going to avoid braces wherever possible, so I may shorten the ST length just a bit, and lower the TT a bit and call it good.

Pretty excited I don't need to brace with those dropouts- I like how they have the brakemount and hanger built in to keep things a bit more simple for my first build.

I will keep you guys updated! Thanks again
 

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The cat's name is jake
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Here's a bent 1.5" DT.

NOVA CRMO 38mm DOWNTUBE FOR MTB/29er WITH BEND :: 38.1mm DOWN TUBES :: ROUND TUBES :: MAIN TUBES :: TUBES STEEL :: Nova Cycles Supply Inc.

I've used it - it's alright.

For entry level seatstays, I'd consider something in the neighborhood of .035". Dead easy to work with in multiple ways - easy to bend, easy to weld, easy to source material. Durable thickness for most types of riding save the most aggressive.

Regarding sagged vs. unsagged, I personally work with the unsagged measurement, just because that's the easiest for me to work with and think about, experience wise. I know what a bike with XX head angle, and XX fork travel/A2C feels like. I think that is most typical, as far as listed figures are concerned.
 

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Discussion Starter · #11 ·
Here's a bent 1.5" DT.

NOVA CRMO 38mm DOWNTUBE FOR MTB/29er WITH BEND :: 38.1mm DOWN TUBES :: ROUND TUBES :: MAIN TUBES :: TUBES STEEL :: Nova Cycles Supply Inc.

I've used it - it's alright.

For entry level seatstays, I'd consider something in the neighborhood of .035". Dead easy to work with in multiple ways - easy to bend, easy to weld, easy to source material. Durable thickness for most types of riding save the most aggressive.

Regarding sagged vs. unsagged, I personally work with the unsagged measurement, just because that's the easiest for me to work with and think about, experience wise. I know what a bike with XX head angle, and XX fork travel/A2C feels like. I think that is most typical, as far as listed figures are concerned.
Thanks! That's the DT I wanted, but it's out of stock. I thought the smaller diameter but same thickness would suffice, but I'm going to stick with the advice here and find something beefier. I'll shoot Nova an email and see when they expect to have more.

I'll check out thicker seatstays, maybe even try tackling bending my own? I have access to lots of woodworking tools, so creating a jig and bending them does sound kind of fun- as long as I don't destroy too many in the process! :O

Unsagged is easier for me to wrap my head around as well.
 

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Discussion Starter · #13 ·
TIG practice!

So I have the notcher pretty much running well, the only thing that is difficult is getting the height dialed in perfectly. The tubing I'm using for practice at the moment is a downtube off of an old GT Timberline, which claims to be chromolly on the ST badge. Thickness measures at about .030", probably from all the sanding to remove the paint. I'm cleaning it up until it's shiny with emery cloth, then filing the burrs off of the inside, cleaning the cut up slightly with a file, and knocking down the paper-thin outside edges of the cut until they appear to be "normal" thickness. 15CFH argon, with a gas lens, 1/16 tungsten (purple-shop didn't sell thoriated anymore) on an older miller syncrowave (250?), set at around 40 amps.
weld3.JPG

I'm having a bit of trouble with my puddle wandering on me, and have checked that I have enough argon, and I thought the metal was plenty clean. The other tip was to make sure the machine is on DCEN, which it is. Is there anything else that could cause this?
weld1.JPG
As far as penetration, I know the picture isn't great, but does it seem reasonable?
weld2.JPG
 

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The cat's name is jake
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Does your Sync 250 have a pulser? If so, use it. If it does not, I would manually pulse with the footpedal. When pulsing, you will need to set your machine to a substantially higher amperage - how much depends on how you are pulsing. My suggestion is to pulse a higher amperage, for a shorter time, rather than a lower amperage, longer time pulse (however you do it).

You have PLENTY of penetration there, but you are really cooking your material. Part of that is exacerbated by the short tubing sections, as they have less head sinking capability. Again, my suggestion is to work quickly, rather than slowly. Welding faster often requires more amps, but in the end, the heat input is drastically lower. All that just comes with time and practice, but knowing that moving quickly is preferred over moving slowly might be able to help you out some.

Try this - If you don't have a pulser, start by running your machine at 85 amps or so. Make your fishmouth cuts, but don't file them back much - you can file the ears back a little where they get really thin, but don't go until they are exactly the same thickness as the rest of the tube. Tack your little practice piece, then start welding by pushing the pedal all the way down quickly, filling the puddle, then backing off to as little as you can without dropping the arc. Then repeat the process, trying to make the second puddle the same size as the first. initially, shoot for doing this around 1 pulse per second. Maybe find some classical music on You Tube at that speed. Practice that for 10 sets or so. You may need to fiddle your amperage on your machine to do this. The idea is that the bead opens up to the correct size (about 3mm or so) at full on, and then you back off to next to nothing as soon as it's the correct width. It will require the most amperage when the joint is closest to 90 degrees. As it backs off to 0 degrees, you will need to either have the pulse on for a shorter time, or not put the pedal fully down. If that doesn't help you any, let me know and there might be some other strategies to try.

For scrap, consider just purchasing tubing from your local steelyard, or from Aircraft Spruce/Wicks. I'm sure there are lots of us around here that have scrap we could send your way as well. Dealing with old paint is crummy business, in my opinion.
 

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Discussion Starter · #16 ·
TIG round 2!

BungedUP,
My machine does not have a pulser- I wish it did! Thank you for the suggestion! I definitely don't have it dialed yet, but the pulsing with my foot is a cool trick. It just clicked in my head the way you mention it. I've had to weld not-so-good fit up with the MIGwelder, and I essentially do the same thing, and I actually like how it makes the weld look better than the regular old MIG weld.
So anyway, I went and fit up some more joints with less taken off of the ears:
weld6.JPG
My first try was too hot, or so it seemed as I was welding, so I turned the amperage down incrementally to about 50. In this picture you can see my previous welds, next to my first try at pulsing, which looks like it overheated less. Penetration is still looking excessive too.
weld4.JPG
Next joint I tried even lower amperage at first, then realized I was compensating by turning it down, not speeding up. So at the very end of my time, I had a good little run of going way faster than I usually do, with amperage at about 60. However, I think I already had cooked the piece by that point.
weld5.JPG
I feel like the pulsing is helping, because the shoulder and ripples seem a little more consistent. It also gives me a bit of a rhythm to follow, which really helps when me when I weld. I'm excited to get back and do more!
Thanks again for the tip, I contacted Walt about some scrap, and will see about buying some fresh tubing locally.
 

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The cat's name is jake
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Dudeman,

Try spacing your puddles out a little bit. Below is an example of what you might try to shoot for spacing wise. You want to make sure that your new puddle covers the previous puddle's crater, by 25% or so. Sometimes I'll stack closer together, but when learning, it's tough to space things out, and do so evenly. The tendency is to stack puddles closely, and move too slowly, which in turn burns the meat! It's just down to practice really, but I think we can get some improvement to the point that you'll be happy, without too much additional effort.

The pulse action should be quick - like a pedal stab, not so much a foot rock. Imagine that you are Neil Peart or John Bonham playing the bass drum. It might be a tough job to get that down in the beginning - just do the best you can that way. Think "HEAT - mooooovvvvve, HEAT - mooooovvvvveee".

-Peter

Puddle spacing example 1.jpg
 

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Discussion Starter · #19 ·
Also, what size filler rod are you using? I'd recommend .045" rod.
I'm using 1/8" er70s- but just ordered 1 lb of mostly .045" weldmold 880 from Walt.
I had one other question- as I was pulsing, I had the torch go out completely a number of times. Is there anything bad about that? It was easy enough to start back up, but I don't want it to mess things up.
I'll try moving further between each pulse in the morning. Your weld is amazing! I printed it off for motivation and something to aspire to.
Love the John Bonham visual too! I'll try stabbing the pedal- I was definitely just rocking the pedal back and forth.

-Scott
 

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The cat's name is jake
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Hi Scott,

FYI - the Weldmold 880T is, according to Weldmold themselves, 312 MIG wire that they straighten and cut. A coworker and I have been working through some filler rod issues, and received some samples from Weldmold. I found that it does some things VERY well. Particularly, it is very good at filling in areas that tend to be undercut otherwise. It also is a little easier to control than 309L when welding 17-4 or 316 stainless to 4130 type steels. However, I am not quite as hot on it for general purpose welding, though it does ok. It lays flat in the middle of the puddle, but it stands proud at the toes of the weld in many cases, which I don't particularly like. It is a very small amount, and is most likely not an issue for most people. I may change my mind over time with it, but currently, I prefer a good quality (Korean) ER70S-2, and ER70S-6 for welding appearance. Either rod in most cases is entirely sufficient for the joint designs of bicycle frames, though the "880T" theoretically has the higher yield.

I'd try to keep the torch from going out, if you can. Your goal isn't to completely freeze the puddle - You don't want to stack one cold puddle on top of another cold puddle. You want to stack one puddle on top of a cooling puddle, which is most likely largely frozen, but not entirely. It's like the puddle is a jelly filled donut - the jelly is the wet part of the puddle.

What I do really isn't all that amazing - it's just a lot of experience. Most people are capable of that, given time. I've spent a lot of time doing what I do - the amazing stuff is when people like you wade into this for the first time, and come out with something awesome. THAT to me, is where magic happens.
 
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