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Discussion Starter · #1 ·
Hi all, I'm looking for some advice from those who have been there. I'm nearing completion of my second frame, really enjoying it and want to progressively start tooling up to maybe eventually build frames for other people.

My question is:
- Is a mini mill the "right" next tool for me, or something else?

My current setup is:
  • Cut miters with printed cutout -> angle grinder -> bench grinder -> dremel -> sandpaper
  • Jig, what jig? I have been building basically without a jig, my builds are pretty straight, but the rear triangle especially is really, really difficult for me
  • BikeCAD free, take a screen shot and send to a printer for a full size render
  • TIG

My big pain points:
  • Mitering CS/SS, other joints are fine
  • Jig of rear triangle
  • Design to fabrication (using the free version of BikeCAD)

What I see as options for next larger purchase:
  • Mini mill. Don't have room for a full size mill. This should allow me to miter and build the pieces for the frame jig
  • 8020 frame jig (or another jig). I could build a jig and have a local machinist make the milled pieces for me
  • Lathe: Could use for miters and would be helpful for making a jig later
  • BikeCAD Pro: Would simplify a lot of things for the build, but current process gets it done

So, that's where I stand. I am ready to start spending some money on everything and don't want to make a decision that feels like I will regret later if I am building frames for money. I'm leaning toward buying the Mini Mill to start as I have seen a number of people using them around to fine results and start to build the tooling for the CS/SS jigs, as well as for building a frame jig.

Thats what I'm thinking, thanks in advance!
 

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For me, your money is best spent on a decent fixture. Being able to accurately and repeatably produce the correct geometry is high on the priority list. Being able to notch tubes is not “that” important. It can be done by hand (or with handheld tools), to an incredibly tight tolerance if you have a fixture that allows you to easily test fit the tubes together in a repeatable accurate position. A good fixture will allow you to set the geometry on the fixture, and hold its position. Then you work towards that, checking later against your drawing. For lots of forms of metal fabrication lathes or milling machines are very nice to have, but main priority would always be a good fixture (which opens another discussion entirely)
 

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Is a mini mill the "right" next tool for me, or something else?
I'm at about the same stage as you and asking the same questions. Biggest difference is that I built a basic jig out of 8020 (and some 3D printed parts and hand-cut steel plate) for my first build. It's not brilliant, but it's better than nothing and it was cheap. I also got a basic mitre tool and made my own SS/CS mitring jig which do the job but could be better. I'd come to a similar conclusion to you: buy the mini mill and it opens the door to better tooling (plus a whole lot more besides). I don't know if this is the best decision but a mill does seem like a more worthwhile investment than a similarly-priced off-the-shelf jig at this stage.
 

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Mini mill is too small to be helpful for miters. Mini mill is too small for much of anything. I have one, I do use it sometimes, like for drilling water bottle holes. It's useless for mitering. A real Bridgeport with a tilting head and all is a different story, but I don't have space for one.

Lathe is indispensable. Lathe is the ur-tool. I cannot imagine not having one, but then again I make a lot of parts that others don't make (hubs, axles, false axles, crank spindles, seat collars, ) and I don't mean a mini lathe either. Lathe can also be used for mitering, however unless you are doing repeated parts, it's probably not much faster or more accurate than hand mitering. I have a mitering jig and I do use it but normally finish with a file anyway so once you count the setup time...the mitering jig is not key. This changes completely if you are doing batches or volume work of course.

Your post failed to mention files. Realize that half of what you probably want to do with a mini mill or a lathe can be done faster with a GOOD file collection. Instead of spending $1000 on a mini mill try spending $500 on a really good set of WELL ORGANIZED and SHARP files first.

I have a basic homemade jig, it does come in handy but about half of its function is holding things up to be worked on, and brazed, since I have it mounted to an articulating tripod head. A good articulating tube clamp/bike stand would be as good or better than a jig for that function. The alignment functions of the jig can be done on a flat table. Actually, even if you have a jig, you will need to check alignment on a flat table anyway, so again the benefits of the jig then become just holding things together while you tack. This assessment changes completely of course if you are making batches or doing higher volume, then having good fixtures is the single most important thing.

Hate to break it to you but rear triangles are just a pain. You might think you can create perfect fixtures to magically miter everything to Just Fit the First Time, and save you the pain, but then you are spending your time making fixtures and setups. It won't pay off unless you are then going to be able to crank out 10 bikes without having to change that setup. So you should probably let go of that dream and get better at hand fitting. Did I mention how important good files are?

Designing is very important, very critical. Designing bikes and building bikes are basically two different fields. Then, further understand the distinction between designing (the bike) and drafting (technical documentation describing how to build the bike). Designing is a creative act, drafting is a technical act. Ask yourself what you are doing, and if it's designing, design until the creative act is fulfilled. If it's drafting, stop now because you don't need to get fancy with drafting, at least for small batch building. If you are going to go build that bike by hand, rather than set it up for automatic/CNC or something, then a few paper drawings or printouts are sufficient to build the bike to the design. Actually you could probably write what you need to know on an index card really. Now I use some parametric CAD software to design, but paper worked for hundreds of years and worked for me for a long time too. Making a fully realized 3D-whatever is important IF that serves you in designing, but is not important in a drafting sense if you are going to go make it by hand, you are just sinking time doing drafting that you don't need. That drafting time is critical in volume manufacturing because it will pay off later in the automated/CNC manufacturing or outsourcing that it will enable and that drafting time with be recouped, but for small batch building a 3D rendering of a joint buys you nothing in terms of building that joint; you just need to know the tube diameters and angle of the joint to build it. So if you are trying to improve you designing capability, and you think software will help, invest in software, but it will not improve your building or make building easier probably. Also, if you understand the value of iterated design+build, it becomes even more important to avoid spending too much time on setups or drafting.
 

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I agree that the mini-machines run out of oomph when you really need it. You would get a lot of bang for the buck by learning 2D CAD with LibreCAD (free) not just for drafting your frames, but it also opens up a lot of opportunities for parts made with laser or waterjet cutting. Even though I have a mill I've been doing a lot of laser cut parts because it's so easy to upload a design and get the parts on your doorstep a week later.
 

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Discussion Starter · #7 ·
Thanks for all the thoughtful replies!

In principle I agree with the fixture being the most important piece from the start. The problem, however, is that it is a chicken and egg, where I don't have the coin (or desire) to drop $4k+ on a prebuilt fixture, and pretty much all the DIY fixtures out there require some machining work. That's one of the reasons I was thinking of the mill route. That is where I am leaning honestly and why I ask the question - I have a long winter in front of me and could spend that time building the jigs and fixtures and learning the tooling. A problem with that approach is the cones which would require a lathe, but I could probably get away with doing something else there.

Mini mill is too small to be helpful for miters.
I agree that the mini-machines run out of oomph when you really need it.
That's what I have read in a few places and is the big reason why I didn't just order one and am asking this question. I have seen a number of people on YouTube using them for seemingly good results (but of course, its YouTube and not everything is shown). I have nowhere near enough room for a Bridgeport, but could maybe get something in between that doesn't take up a ton of room in my garage.

Designing bikes and building bikes are basically two different fields.
Totally valid! I am currently focusing on the building aspect and not trying to do anything "creative" on the design with the exception of building what I want.

Your post failed to mention files.
Honestly, I'm not interested in working with files. I'm pretty proficient/quick with being able to cut them with my current setup with the dremel - it's the compound angles (like the ovalized seat stays that I have to freehand) that are throwing me off.

You would get a lot of bang for the buck by learning 2D CAD with LibreCAD
Totally! In my welding class at the local high school they had a CNC plasma and I did some 2D CAD for a hitch bike rack I built. It was so cool, I'm looking for other things to do with those
 

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That's what I have read in a few places and is the big reason why I didn't just order one and am asking this question. I have seen a number of people on YouTube using them for seemingly good results (but of course, its YouTube and not everything is shown). I have nowhere near enough room for a Bridgeport, but could maybe get something in between that doesn't take up a ton of room in my garage.
Everything you see on YouTube about machining should be completely ignored. Almost every 'influencer' I see there is either a shill or an imbicile. There are some good sources there but they aren't talking about mini-mills.

There are a lot of ways to solve your problem.
1. Do you really really not have the room for a Bridgeport or are you just not willing to do the work to get one into a tough place? A full size Bridgeport will fit in most basements...you just need to move it in peices. Also, look into VFDs.
2. Don't you know people that have a mill in the corner of their shop that you could 'lease' for a few projects? Do them some favors?
3. Often, a local school class leads to a bunch of 'free' machine time.
4. Maybe there's a maker space.

Really, I shared a link to those plans for a state of the art fixture that is super easy to make and costs about $850 to make. If that's too hard for you then you've got other issues that are far more important to focus on than framebuilding.

 

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A problem with that approach is the cones which would require a lathe

These are cheap from the EU and slide nicely on 16mm drill rod

You can also locate a cylinder on its ID by three pins on a flat plate, or on its OD with a v-shape.
 

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I'm a new framebuilder and have both a mini-mill (70s-era Jet 8x30") & frame fixture (very used Henry James Access 65). Both have been very valuable to me! I have a super small shop space and will probably move soon so getting a full-size mill or lathe would've been logistically impossible. A smaller mill will certainly help you learn how to machine and you can get work done within the constraints of whatever system you have. There are also services like Xometry & local machine shops that you use for more complex jobs.

Especially if you're using the mill just for notching, drilling, and light aluminum machining you don't need a literal ton of steel in mass. Some mini-mills are very far on the mini end of the spectrum and won't be much use, but there are Grizzly/Jet/off-brand options out there that will be plenty rigid.

Lots of people get hung up on doing things the "right" or "best" way but you need to work within the constraints you have and focus on the parts of the process you like the most! Part of the joy in building is being creative within your unique set of circumstances.
 

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I don't know where you draw the line, but to me a mini-mill is like a 4x16. An 8x30 or one of the 6x26 bench knee mills would be enough for garage framebuilding where a full 9x49 Bridgeport might be too tough to move or justify the money.
 

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I have small benchtop mill, 1hp same mill as the Grizzly G0704, uses R8 tooling.





You certainly can cut any and all bike related miters on it. Is it as rigid as Bridgeport? Nope. Finding a used full size knee mill locally here in Vancouver BC that fits the same budget is next to impossible, so the benchtop was the best option. I have no regrets, I find using it much more enjoyable than file miters.

This winter I am probably going to build PVD's Skynet fixture on it. Will report back on how it goes. Understand that it's a smaller tool and needs to be used accordingly.
 

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As an owner of a refurbished HF mini-mill, I would say no, it's not worth it as a mitering machine. I received this one for free, but I would never pay the retail price tag for this hunk of crap. I destroyed the plastic drive gears the first time I tried to miter a serious tube. It has since been torn down and rebuilt with new bearings, belt drive, etc. but I still find it lacking for actual framebuilding. I did use it to machine all my own parts for a 8020 fixture, and it's happy chipping aluminum and small steel parts. At least with the tiny vise I have, there just isn't enough working space to be comfortable. I'm going back to hand mitering for now, until I can get a full size machine. I think a bench top knee mill could be a little better, but haven't used one personally..
 

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If I were to buy things over again (and if I still had the space I once did) I would buy or fabricate a fixture first and a decent lathe 2nd (check out Precision Mathews).

Then I would buy one of those tube notchers from Medford tools (Syncro 180 Jr or whatever) — they work for everything except the seat stay notches and are rigid enough for a newbie.

. . .

but going back that far I would've also spent the first 6 months of my time notching tubes by hand and doing 100+ joints/month. That investment would've saved me enough time/money to afford better tools when I started making frames.
 

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Years ago I had a mini mill, here's my experience...

Right after I graduated I had little space and thought it'd be fun to get a mini mill and convert it to CNC (500W spindle, seig clone, don't remember size off hand). I started building bikes years later and did use it in the beginning for 8020 jig jig parts and mitering. Did it work? Yes. Was it fun? Yes, at first, but it became painful. In order to put a hole saw through a tube I had to run it at a minimum of 600+rpm or it would stall, which sounds horrible and really expedites wear. It was near impossible to get the machine square (particularly I could never get X truly perpendicular to Y). And the rigidity was very lacking.

Could I work within those constraints? Yes and I did for a while with lots of patience (minimal tool load, slow feed rates, constantly checking and adjusting many parts of the machine), but ultimately the thing ended up in the trash and real tools were brought in. I'd say I'd have saved time and money buying real tools in the first place, but bike building wasn't my intent then and space/money weren't my reality; so I started with the mini mill... These days I buy the absolute biggest thing I can possibly fit and have not regretted that strategy.
 

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Hey guys,

I'm not a frame builder. My day job have is mechanical engineering design. I also own company on the side manufacturing mountain bike racks and fire pits.
www.plummetindustries.co.nz

I agree with the others on one point. Make yourself an adjustable jig. That will be critical to tack up well aligned frame.

For designing the frame and creating profiles to cut I suggest you look at a program that can export DXF files for sheet metal and step files. Fusion 360 is the best/lowest cost option for 3d modeling.

Now regarding tube notching. Look closely at subbing this out to a tube laser company. A tube laser will cut the exact notches you want (assuming your model is accurate) typically at a price that is so cheap you cant manually you cut it yourself for that price. As with anything cnc set up costs increase the per part price for low volume. So if you are going to make multiple bikes it getting tubes cut in bulk saves cash.

The same goes for any sheet metal parts you may want like gussets etc. Model them, export the dxf's and reference drawings. Send it to a flat bed laser cutting company. For anything complex laser cutting will be far more cost effective and accurate than manual cutting/shaping if you are charging your time out on a build to sell to others.
 
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