# Placement of slotted disc brake mount on horizontal dropouts



## illcomm33 (May 10, 2006)

Just wanted to understand the correct placement of a slotted disc brake mount when using horizontal dropouts.

My intuition was to place the Anvil Feng Shui in the center of the horizontal dropout and also center the disc brake mount in the jig.

Problem I see now is there isn't enough material contact on the dropout so I planned on filling down the mount (check the sharpie lines) to lower the mount and provide more contact. Flipping the mount around didn't appear to work at all.

Thanks for any advice!


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## febikes (Jan 28, 2011)

If you move to the chain stay it looks like the mount you have "should" work but you may need to tweak your setup because it looks like the fixture you have does not allow it to setup in that position.

You need a different mount for mounting on the seat stay.


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## Walt (Jan 23, 2004)

The slots on the mount need to be roughly parallel to the slot of the dropout. Otherwise your caliper won't actually adjust with the wheel. I'd start with the dummy axle at the front of the dropout, and with the disc mount likewise set up so that you've got a usable range from the front of the dropout to where the caliper adjustment can't go anymore (less than the full length of the slot, c'est la vie). 

_Walt


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## illcomm33 (May 10, 2006)

Thanks for all the replies and advice. Now that Walt mentioned the slots need to be as close to parallel as possible that picture looks ridiculous. 

That slotted disc brake mount is from Nova..and the HJ one is pretty similar. Where would I look for a different style? (just checked Bikelugs and didn't see anything)


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## ktm520 (Apr 21, 2004)

You need something like these for a seat stay mount.

STEEL ISO DISK BRAKE MOUNT :: SMALL PARTS :: BRAZON/SMALL PARTS :: Nova Cycles Supply Inc.

www.paragonmachineworks.com - BK2006SteelISOCaliperMountUniversal14HiLo


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## jgerhardt (Aug 31, 2009)

I fabricated something that has worked for the past 2000 miles on my commuter...
If I did it for someone else I probably would beef it up a little.


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## illcomm33 (May 10, 2006)

KTM520: I actually have one of those mounts (NOVA) but was under the impression that they shouldn't be used with horizontal dropouts. I have done it one time before (SS 29er, HJ MTB track dropouts...it was a beltdrive so I knew approximately where the rear axle was going to be) and was just about ridiculed by a guy at the LBS for doing so.

That is a slick design jgerhardt (actually the entire rear end is awesome)...well done!

During some web searching and I come across a pic of slotted tab that Kirk Pacenti did make at one time....but is out of stock.(?) 
https://www.bikelugs.com/_uls/store_items/ADJUSTABLE_DISK_TAB_resized.jpg


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## Walt (Jan 23, 2004)

Get creative - cut up that sucker you have and weld/braze it back together to make it the shape/configuration you need! Nobody said you can't whack it into bits and put it together some other way, or add some more material somewhere. Hell, the two slots don't even need to be connected like that - the seatstay and the caliper/adapter will do the job of keeping everything together just fine.

BTW, the brazing looks killer! How about pics/info on the rest of the frame?

-Walt


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## ktm520 (Apr 21, 2004)

Duh, my bad.


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## dr.welby (Jan 6, 2004)

There are also solutions where the top slot is parallel to the seatstay and the bottom slot follows a curve. You could braze the top half of that mount about where it is, braze a blank plate at the bottom, then use the disc brake jig to mark where the bottom bolt will be as the axle position changes. Drill out those holes and file them together into a slot.


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## DWF (Jan 12, 2004)

What Dr. Welby says. If you draw it out you can figure out how to place the slots so that the caliper is always properly positioned on the rotor no matter where the axle is located in the slot. As Walt said, cut that mount up and use the pieces to make it be what you want it to be.

Like this:


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## dr.welby (Jan 6, 2004)

The bottom slot can be straight and the top one curved instead (if the bottom isn't parallel to the dropout slot). 

There's probably enough tolerance that both could be straight slots, especially if you're not going to be running a huge range of gears. If you really only run one gear, having the should-be-curved slot straight and tangent should do the job.

One thing you'd like to avoid is positioning your brake far enough behind the rotor that the caliper blocks you from removing your wheel...


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## restlessrider (Nov 29, 2007)

I think you could flip it around so that the little tab touching the ss in your pic is touching the top of the d/o instead, then cut an angle to mate to the ss. That would orient the slots in line with the d/o.


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## illcomm33 (May 10, 2006)

*Installed*

Just wanted to follow up with the final product.
I again appreciate everyone's guidance/recommendations!
I really wanted to make sure one of the braze on tabs fell on the dropout vs 2 on the seatstay. I know (from several past experiences) that I will need to use CPS spacers/washers to get the back end of the caliper up. Live and learn I guess.





















This is frame number 18 and going to be a 650b SS Belt Drive demo.
Thanks again! Walt I am going to send a follow up email about the seat tube sleeve...got some issues. ;(


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## Walt (Jan 23, 2004)

It doesn't look like you used a sleeve... or do you mean you are having a problem *because* you didn't use one?

Disc mount looks great!


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## illcomm33 (May 10, 2006)

Thanks for the quick reply and comments Walt! I figured I should just post the sleeve/seattube question so others might benefit and hopefully give you a break from answering all my questions.

This is the first time I used a sleeve for the seat tube...been using external butted (1.2) Nova seattubes with good luck. _(Still slight distortion...but manageable)
_
This is a small frame and I realized the external butted seat tubes I had on hand (or even available via Nova) were so long that to cut it down to 355mm would leave me brazing on .6 walled steel.

I instead, for the first time, used the Aircraft Spruce 4130 steel that I normally use for my bent/curved top tubes (4130 STEEL TUBE 1-1/8X.035 wall) for the seattube with the thought that a straight .9 wall would be a better bet than .6.

Issues:
1) I have a Cyclus 27.2 seat reamer that I used (it was a lot of effort) to ream down 150mm into the seat tube. It took a long time and a lot of cutting fluid.

I can't get a 27.2 post to insert completely past the sleeve. I went to the LBS and tried a 27.0 & 26.8 post. The 26.8 post inserts (27.0 was also a no go) and can actually be clamped in place with the 30.6 seat collar even with the initial slop at the to of the seat tube from reaming at 27.2 .

Pics attached. The Nova sleeve doesn't cover the entire top tube junction which I assume is part of this issue. I did silver braze that sleeve in place before brazing the TT and ST.

What to do? 
I don't necessary want to ream anymore material...and make the tubing even thinner. *Should I just use a 26.8 post and call it good and never use this approach again? *

Is using a non-bike designed seat tube a bad idea? Is that Aircraft Spruce tube not as quality as a Nova/HJ seat tube?

Are my fillets too large and causing more distortion?

I am pretty sure Garro uses a sleeve about 1.5-2 longer.

Hope this makes sense and also helps someone else out.


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## dr.welby (Jan 6, 2004)

1.125" OD - 2* .035" wall = 1.055 ID = 26.797mm ID

So realistically you should have used a 26.6mm post, maybe 26.8 if you don't mind reaming.

Can you ream it to 27.2? Sure, and it's going to suck. Do it in small batches, listen to some good music, apply Attitude Adjustment of choice.

This isn't about removing distortion - you are manually boring out the tube to the proper inside diameter.


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## Walt (Jan 23, 2004)

I think you misunderstood some things about what the sleeve is for.

-Start with a tube that is the *correct ID* (a little big to minimize reaming) for the post you want to use. In your case, that would probably be a 28.6x.6mm wall tube with a .9mm section at the bottom to join to the bb (ie any old single butted seat tube).

-Since the .6mm section is too thin to join directly to the toptube or seatstays, sleeve it with an appropriate ID/length sleeve. In your case, it looks like you made the sleeve too short to really support the joint. 

Reaming should really just be to remove distortion from joining and/or oxides generated by all the heat. It's not a great way (as you've discovered) to change the original ID of the tube.

-Walt


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## illcomm33 (May 10, 2006)

Thanks Dr W/Walt for the detailed explanation/thoughts. I am shaking my head right now in frustration with my mistake. Going to have some bad dreams over this one. 

I have always been accustomed to the double butted/external butted tubes* where I would alway have .9 at the BB. 

Again I really appreciate you taking the time to share your knowledge.


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## dr.welby (Jan 6, 2004)

illcomm33 said:


> Also I never really thought about flipping a single butted seat tube around to use the .9 on the bottom bracket and the sleeve (with a much longer sleeve) the .6 top.


That's not flipped - that's the right orientation. The traditional 9/6 seat tube is the standard lugged seat tube, and you *need* the .9 at the bottom bracket for strength. The .6 upper would have been supported by the seat lug. It's single butted to give you adjustability over a range of frame sizes. In this case the thicker part has nothing to do with the seat post.

Fast forward to TIG bikes and modern mass production. The seat lug/sleeve has been integrated into the seat tube by externally butting the tube. This saves a step of having to reinforce the tube though as you discovered, it limits the sizing. But the .9* still goes on the bottom!

* or .8 or .7 depending on your alloy. But not your .6, .5, or .4.


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## illcomm33 (May 10, 2006)

Thanks Dr Webly. I should clarify that I have actually never used a single butted seat tube so I never used .6 on the BB. I will correct for clarification.


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## Francis Buxton (Apr 2, 2004)

illcomm33 said:


> This is frame number 18 and going to be a 650b SS Belt Drive demo.
> Thanks again! Walt I am going to send a follow up email about the seat tube sleeve...got some issues. ;(


How are you going to get the belt on? It doesn't look like you have any split couplers or a split dropout. Maybe I'm just not seeing it in the pics?


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## illcomm33 (May 10, 2006)

Francis Buxton said:


> How are you going to get the belt on? It doesn't look like you have any split couplers or a split dropout. Maybe I'm just not seeing it in the pics?


Thanks for the question. I fabricated a dropout plate using 11g 304 stainless steel and countersunk for the 6-32 stainless screws. I cut the Surly dropout using a very thin hacksaw blade to reduce the kerf.


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