Best tools for speeding up fillet finishing process

Hi all, Im looking to speed up my process for making my fillets look nice and smooth. I have been using files and sanding paper until now. But as I want to speed up I have started to use these tools:

– Belt sander
– Grinding bits

What are you guys using?

Practice welding more. Then you can get to a point where clean up is just a round file wrapped in emery cloth. Besides, the welding practice is more important than having tools to clean fillets.

If that doesnt work for you, very careful work with a dynafile can be great. But also a great way to undercut welds and potentially destroy a frame…


I also use files and sandpaper. Edit: emery cloth in a roll. 3M 80 grit from framebuilder supply is better than Nodton 80 grit, in my experience.
Paul Brodie uses a die grinder with a sandpaper cone in the collet. He starts talking about it in this video, about 24 minutes in: How to fillet braze - From start to finish with Paul Brodie - YouTube
After the die grinder he switches to a hand held belt sander of his own design, similar to a dynafile.
The best way that I’ve found to speed up the finishing process is to lay as smooth of a fillet as possible. The on/off style that’s popular on instagram is a lot more work to finish.

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Welding as in TIG welding or practice brazing more?

Slow parts are for me always bottom bracket and seat stays. Narrow and hard to get smooth I think.

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Keeping in mind that I have only rarely fillet brazed bike stuff (I’ve actually mostly done it for steel furniture where friends wanted the cool gold “weld” look), my suggestions are:

-Emery cloth>sandpaper. If you get the frame in the right position where you can pull on a strip of emery cloth, you can really sculpt/smooth pretty fast in some situations.

-Good work holding, as mentioned before. Set yourself up with a stand bolted to the shop floor where you can hold the frame really well at a variety of angles and heights to make sure you can comfortably get purchase/pressure/leverage when you need it. If you’re holding the frame in your lap or bending over and killing your back to reach what you want to reach, that’s bad.

-Files - but not just any files. You are going to want to go redneck on some of your files and grind smooth one or more sides to get you something you can use in tight spots without the risk of damaging nearby tubing. Experimenting with an open mind (use cheap files from a garage sale to start) is the key here. Also really useful for slotting stays - a flat file with only the short axis toothed is a great tool to have, so get out the grinder and teach those files who’s boss!

-Jewelers files are great for tight spots too (and other stuff).

Finally, you can always learn to TIG weld and then you don’t have to finish the joints at all.



I use a Dremel with 1/2" 80 grit spiral sanding rolls (McMaster #4688A613) to quickly shape and smooth the fillet. I bought an electric dynafile and it works well but it’s so big you can really only use it on maybe 20% of the fillet work on a frame.

I also use round files with and without a wrap of 1" emory cloth depending on the spot.

On occasion I need to use a little grinding bit on my dremel to get in a tight space.

The hardest part to sand smooth is the edge between the bronze and steel. I try my hardest to really make the bronze flow so the transition takes almost no cleanup.

I’ve said it before, but for the longevity of your frame, I don’t recommend leaving a defined edge on your fillets. This edge is a potential stress riser. I’m likely being very conservative here, but IMO unfiled fillets are dangerous. So is undercutting when cleaning up your fillets. I think cleaning fillets takes more skill than laying them down.


I can follow that sentiment. Thanks for your input. I do get a lot of satisfaction out of seeing these nice smooth fillets. Then I paint them over and nobody will ever know about all that work :smiley:

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Just ordered a set of needle files. Thanks!

I used a die grinder with tapered cartridge rolls. 15ish years ago it cost me about $100 for a cheap but decent pneumatic grinder and the cartridge roll kit.

You have to be careful not to undercut the steel.

I saw that Milwaukee is making an M12 narrow belt sander. I might get one of those now.

Lots of practice really reduced my need to sand down fillets.

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Haha, so true. That’s why I’m moving to TIG. I can’t wait to not file fillets :partying_face:


This is the trajectory most people end up on who want to build as a business - and even high volume hobbyists. That, or they just stop filing the fillets altogether and learn to love the various levels of lumpy mess.

Fillet is awesome for being inexpensive, allowing any angles you want, and being super easy to learn (I used to teach people to fillet braze well enough to build a safe frame in about 30 minutes in my class). It also looks cool as shit.

But if you want to build bikes at any reasonable speed, it gets old real fast.



You can also, hear me out, just not file fillets! I don’t and it’s great.


I’m with @manzanitacycles on finishing fillets. I think it’s an essential part of the process if you’re going to fillet braze a long-lasting frame. Building a nice fillet and smoothing out the transitions between tubes is what makes fillet brazing worth doing. I think maybe some people have the skill to lay really perfect fillets that don’t need any attention, but I’m not one of them. The factory in Taiwan that builds Mone frames, and Curtis bikes come to mind.
I have broken a lot of bike parts and a few frames, and I’ve learned to be very afraid of stress risers.


Great stuff. I am still up for brazing soon once I get my oxygen concentrator.

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Check out Master Brodie’s video on fillet brazing:

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Everything is great until it breaks. I value my customers’ teeth more than saving a couple of hours of work.

Maybe I’m being too cautious, but only one of my frames has broken, and it was the only frame I left the fillets unfiled at the customer’s request. It’s not worth the risk.


How are those connected, not sure I understand that?

I’ve never heard of unfinished fillet frames being any more prone to joint failure than finished fillets. If that were the case, then builders would be filing TIG welds for safety.

Brazing and welding are very different processes.

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Exactly, and nobody says that TIG welds need to be filed for safety. So, why should brass fillets need to be filed for safety?