What do you think of this build?
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Side loads can be handled by creating a belt driven spindle .with a draw-bar of some kind.
Figure out your chip loads and what RPM you will want. You will likely find you don’t want any planetary gearing in your spindle. Also consider most drill motors are brushed universal motors that can make a bunch of RF noise. Do you really want to risk finding that it interferes with something when you will likely want some long runtime jobs?
Power output will also be a problem. Spindles will be subjected to long, sustained load at high power, something a handheld drill was never intended for.
Thanks for that input. I’m thinking of how cheap can it be made. What kind of cheap motor could be used to drive a belt to a spindle. My electronics muscle is weak .
I have a dc motor from one of those massage recliners. For a spindle I’m thinking of
a deck spindle from a garden tractor. .One using tapered roller bearings.TIMKEN used to make the best bearings 30 years ago.
Definitely NEMA 23 @Kentamanos. I’ve been wanting to do this for a while now. Really the only thing holding me back has been time and the inevitable “Where will I put it?” problem.
Do you have a BOM going? Maybe a joint, or more, Google Docs effort on the parts to source?
Interesting.
I wonder why the side plates are so thin. Intuitively, I’d think they’d need to be beefier, but that’s not based upon any sort of calculation.
The poured granite machine linked above is fascinating. WAY too big for what I need ( and have space for. ) But very nice indeed.
I have the following thoughts:
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It’s not a mill, it’s a router. It is taking advantage of the very high RPM of the router spindle to reduce cutting forces enough to make such a light construction able to machine aluminum. This is not to say that it isn’t useful, but it surely isn’t a milling machine. For a cheap router I think this is a decent design. Not quite what I would do but not bad.
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This design uses an Aliexpress especial router spindle. The router spindles just don’t work for milling applications. Now, you can get by in aluminum and sometimes even steel for side milling and threadmilling jobs. I.e., large plate work will go well in aluminum, and tiny steel parts will work with some struggle. The difference lies in between how the spindle is constructed and how the drive motor is configured. The construction: the bearings are very small and there aren’t many of them. This greatly reduces the stiffness of the spindle. Second, the material use–the housing is aluminum while the bearings and spindle shaft are steel. This means that the housing will differentially thermally expand more under load and cause the bearings to loosen, which is very bad for stiffness. Spindle motors like that generally will do between 6-24000 RPM (Any lower than 6k RPM is essentially useless) and only top out at about 1-2Nm of torque, which is really not enough for milling applications. This is why I recommend using an X2 mini mill spindle, OR the very cheap Aliexpress BT30 spindles with manual drawbar. They aren’t good spindle by any stretch, but I think the cost and performance perfectly match this application.
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Aluminum construction is not a good idea for a milling machine. While it can be done, any aluminum structure will have 1/3 the stiffness for the same geometry as a steel structure. It also has far worse inherent vibration dampening than steel, because of 1. the material properties, 2. its mass is lower for a given shape. Basically, in steel, you would have to use very high quality tooling, and the second there would be any tool wear, your tool will explode because of the vibration.
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The design presented will have geometric accuracy issues because it has the linear guides bolted to mill finish aluminum which is not remotely flat. Because of this it will be impossible to geometrically align it because there is no real reference surface to work from. This may not matter depending on the application but it is something to keep in mind.
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For milling applications the design will not be stiff enough. If you pushed a half inch drill in mild steel with appropriate chipload, you would probably have a bad day. If you side milled perpendicular to those side plates, you would also have a bad day in a normal milling cut in steel. Again, it could work if you were very conservative OR used a high quality, high RPM spindle.
In summary, it’s fine as a router. It will probably be lots of fun, but sadly it isn’t a mill.
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Since we have a full shop and we can machine it on the HAAS, what do you think of:
- upgrading the spindle to your recommendation of most likely the BT30 spindle, redesign the Z axis to handle the increased weight.
- swapping out steel for the aluminum in all structural areas, at least the bottom and sides.
- fly cutting or otherwise truing the surface the linear guides are mounted to
- Maybe adding a “top plate” to give it more rigidity in the perpendicular to the sides direction
With respect to this, if I’m willing to wait for the increase in milling time, what’s the downside to running a 1/8" tool instead of half inch rougher at way lower RPM?
In my mind, I’m willing to work with anything that gives me the Z-Axis I need (around 6") and can cut Aluminum. We can call it a router if you like 
Alternatively, do you have any other project designs in the sub $9000 area that you think would be a better thing to attempt?
With a router you probably can’t get it down slow enough. even my 3hp variable speed router can’t get below 10,000 rpms. The downside - unless you’re running full on flood of coolant you will have a lot of burnt or broken endmills. Quickly. The flip side of this is that you’d have to run the feed rate so slow to compensate you’ll die of old age (or sure will seem like it).
Calvin’s other points have merit and let me add that when you’re running a high speed mill (over 10k rpm) you have to use a balanced tool holder or you end up really lessening the life of the spindle. Or worse, you sure don’t need it throwing the tool at 20,000 rpm with 15 hp behind it.
Maybe the question has already been asked–do we want to build a machine from scratch or just end up with a fun machine to learn with? Both have merits as I will describe below.
If I understand the goal, we want to learn about machine building and give an affordable springboard into CNC. What I think best does that is a converted Sieg X2D manual mill, which is a bargain at a base machine price of $700. This is a well documented path in the DIY CNC community and with the tools we have would be very manageable. I am guessing the cost would total somewhere around $1400.
http://www.migration.g0704.com/Hossmachine.html (this site has aged poorly it seems, but there are plans out there which I could search for later)
You basically just have to make a few aluminum parts (easy in our machine shop) and buy some ball screws, steppers, and build a control box. Do a few simple mods to the original machine, slap the parts on, wire it up, then you have a CNC with surprising capability as you can see in the video below. I think it meets all the original stated requirements except for the Y axis travel (which is only 5")
But none of that matters if everyone here wants to build a machine from scratch. So, to answer your question, let’s get philosophical and handwavy!
Imagine that in designing a machine to optimally be low cost and still justify the cost, you want each component to have an equal contribution to the machine’s usefulness. No part should have extra functionality or less than the other parts. Otherwise there will be waste.
Thinking on this I have whipped up some vulgar, sourceless MS Paint handwaving 
:
The hackaday design is probably to the left of the break even point in the graph. It will have some critical weaknesses, which could each be solved for a modest increase in cost. If all those are done you might end up with this design I have whipped up, complete with BOM cost and links AND shitty FEA!
I estimate that this design is a bit to the right of the break even point shown in my graph, where small additions in cost yield huge benefits to function. For example, the spindle motor I linked in the BOM is 1.5 HP. A 1HP servomotor, while $100 cheaper, provides about half the capability (based on both the power and torque) of the 1HP motor. So, assuming you have the stiffness to use both motors to their full capacity, you lose half your machine’s capability while saving $100. Who wouldn’t spend $100 more to double performance? The same curve applies to basically all the components and leads to greatly increased cost, but it’s very justified IMO.
But, at the end of the day, it’s more than $3000 and is expensive. You could have an X2 CNC conversion for $1500 or so and in most cases that’s all that is needed. Because the parts of a CNC are expensive in single quantity it’s just impossible to achieve the same function for the cost compared to conversion machines when below the $2-3000 mark.
The design I shared would blow that X2 away in machining performance. But if just having the function of milling, learning, and cost is the goal, X2 conversion all the way, all day. Or we could try and come up with a cheaper design too. For a DMS project that is approachable, I think the X2 would be a fantastic experience. Perhaps a full scratch build would be a logical next step after that.
Thoughts?
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I’m down with it. What do other people say? I’m not going to lie, I would be excited about milling the whole machine, kindof like printing a printer, but if it’s cheaper and better to go the X2 route, I’m for it. I’m sure they’ll be plenty of learning whichever way we choose.
Unsure.
The base mill is $699 and $200 shipping. So $900 to just get started.
One of the advantages of a complete DIY approach is that the cost can be spread out over a longer time period. Looks like bigger initial hit PLUS more in the long run. The X2 appears to be a relatively low speed spindle for example. So $900 plus another $600 to upgrade that. That’s without any electronics.
I think I’m more interested in something like the hackaday project. A budget machine that I can upgrade later has advantages to me. Not sure I see an upgrade path with the X2 ( beyond the CNC part ).
Just curious (I’m not considering building a milling machine, no room in my house or my day) - what do you think of the Multimachine? I remember reading about it several years ago in Make: and thinking, some day, when I have a couple old engine blocks laying around, I can make a milling machine… 
It is true that you can spread the cost over time. I doubt that DIYing a machine will have a lower entry cost based on the cost of parts I have presented. But I leave it to the group to decide what to do on that front.
All I want to do is provide insight on the design of machines and how to measure their specifications, and be sure that the group knows how to define what it wants. That way I think we have the best chance of success on what will doubtlessly be an expensive, complicated, but excellent project. These builds, as the Hackaday writer comments, are extremely prone to feature creep (and stagnation). But along that creeping, potentially stagnant journey is a lot of learning. There is a balance to strike.
From here on I would like to step back and let others discuss, maybe help make a few parts or provide cad/cam advice. I already have my own design to work on after all
I’m curious about something on your design. You have the spindle a good ways out from the X axis slides. Seems like that would be less stiff than having it closer. What’s the purpose of the space ?
Also - the granite base. How do you attach the metal parts to that ?
The spindle can’t get much closer because the linear guides and ballscrews need vertical clearance to fit (they aren’t pictured because I was just slapping the design together). As far as spindle projections go, it really isn’t bad compared to many C frame milling machines like the Haas or others, such as this really cool video showing a DMG Mori VMC:
The granite base has holes diamond hole sawed into it and then steel threaded inserts glued in. From what I have read and seen others do this is a surprisingly effective method. Here is Tru-stone, a division of Starrett, giving their specs for their threaded inserts. An M16 threaded insert will sustain 41 Nm of setting torque, ignoring friction that’s 30000 pounds of clamping force (seems strong enough to me )
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Did you order the granite with the holes already in place, or did you have to bore those yourself ?
Did a little looking thru CNC stuff on Amazon.
This looks interesting:
Would require 220V single phase, but that’s doable at home.
Add $129 for a VFD controller. Not bad.
I love this in their description
- Air Spindle Motoring extremely high speed working environment, ordinary bearing can not ensure this high rotate speed for using for long time
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