Need Help!- Manual Vertical Mill Design

[BuckingFastards]

Good day,
I am in the process of designing a manual vertical milling machine, which I plan to build from scratch out of 80/20 extrusions. My design is simple but would like some approval from some of you members on the zone before I plunge into the build.

I would like to have 20” in the x axis, 12” in the y axis and 8” in the z. My main purpose for building this vertical mill this large is because I don’t want to have wished I built or bought a bigger vertical mill in the future. The project I would like to keep on a budget of $400-600 but if necessary will go higher than the budget. I would like for the vertical mill to be as precise as my budget allows. The types of projects I would like to take on our things such as model engine building and hobby projects. I want to build the vertical mill as a manual mill first then in the near future, upgrade it to a CNC mill by just adding the motors, controllers and software.

So now for my design and my question. I would like to eliminate the use of linear slides, or ballscrews on my mill, and just use precision acme threaded rods and acme nuts to control the axis. Meaning I want to weld acme nuts onto a metal plate, bolt the plate to the table and control the axis with the use of a hand wheel (the acme precision nuts will not turn just the acme threaded rod with the use of the hand wheel).

I would like to use these acme precision threaded rods from MCMaster-Carr http://www.mcmaster.com (Model #): 99030A110
(This is the threaded rod description if you cannot search by model number: 1018 Carbon Steel Precision Acme Threaded Rod 1/4"-20 Sz, 1/20" Travel/Turn, 6'L, Rh Thread)
The acme precision nuts that I would like to use are these (Model #): 95072A450

How do you guys think this design will work? Do you think I will get extreme flex in the rods and it would not be worth it to build the vertical mill this way or do you think I can pull it off and the mill will be inexpensive while still being precise?

Please let me know your views about my project.

Thank you

[acondit]

Just from looking at your picture, I would say that you would need extend the head out from the column (so the spindle center is at the center of the Y travel).

Alan

[BuckingFastards]

Thanks for that advice I never thought of that when I was designing the mill. Although my design is still in the beginning stages I will keep that in mind for when I am redrawing the Vertical Mill.
Also in the picture the Y axis is not back all the way, it is not a very good angle though.

[BuckingFastards]

Originally Posted by BuckingFastards So now for my design and my question. I would like to eliminate the use of linear slides, or ballscrews on my mill, and just use precision acme threaded rods and acme nuts to control the axis. Meaning I want to weld acme nuts onto a metal plate, bolt the plate to the table and control the axis with the use of a hand wheel (the acme precision nuts will not turn just the acme threaded rod with the use of the hand wheel).

I noticed I made a mistake in my writing. What I meant to write was that I will use drawer slides on all axis. And control the axis with the hand wheel. How would this work for a vertical mill?

[ataxy]

Originally Posted by BuckingFastards I noticed I made a mistake in my writing. What I meant to write was that I will use drawer slides on all axis. And control the axis with the hand wheel. How would this work for a vertical mill?

drawer slide... no to weak for the job unless you are not thinking of the same type of drawer slide i am thinking

[BuckingFastards]

I was thinking of using three draw slides on the x & y axis and two on the z axis. I would have put two drawer slides on either side of the x and y axis in opposite directions then the other ones in the center. So when one of the drawer slides reaches it's end it will be starting on the opposite draw slide, that way I can have maximum strength.

Just looking at another post on the zone, I saw another potential idea. The link to the owner of this picture is here: http://www.cnczone.com/forums/showthread.php?t=8928

I was thinking I can do just as he did to slide my axis, with steel rods, and still use the precision acme threaded rod to move the axis. I feel this will slide better. Any ideas on how this would work for my vertical mill?

[DareBee]

IMO
You will not be happy with the outcome of what you are trying to do. It will be very floppy when trying to cut and you have allowed no provision for backlash compensation in the screw system.
A spindle with proper speed control will be an issue and this machine will not adapt into a decent CNC in the future.
Sorry - I am not trying to be a dick but I strongly feel that you will be throwing away $600 with what you are trying to do.

I have a knee mill with DRO, X power feed and coolant system for $1500.

Princess auto sells the X2 for 999 and usually comes on sale once a year for 3-4 hundred off.

If it takes you 100 hours to build - you could have worked for $10/hour and have $1000 (minus taxes) EXTRA to buy a proper built machine.

[BuckingFastards]

No, I would rather you to be honest then to lead me into saying I could do something that you think will not work.

Perhaps I should stop thinking of doing this a cheap way and think of the more efficient way of doing things.

How about if I scraped my initial budget and decided to use leadscrews instead of the acme threaded rods? Would this be more precise? Keep in mind I would still like to use the steel rod for the axis to glide on. The thing is I would really like longer travels.

[H.O]

Hi,
Yes, ballscrews might make it more precise but that's not the issue. It's very easy to underestimate how rigid a metal cutting machine really needs to be to be able to cut precise parts and produce a good surfacefinish. The machine needs have mass to dampen vibration and it needs to be rigid in order to not flex due the loads produced during cutting.

I've built a small CNC-macnine out of heavy duty ALU-extrusions, (180X90mm), it has ballscrews and linear slideways. The basic desing is much like yours (but with less travel) with the X-axis on top of Y and the spindle moving up and down on the column. It works, it cuts, but it's not rigid. If you're interested how it looks you can see it here.

The weakest point on mine is the connection between the base and the column. The column stands around 600mm tall and if I grab it and push it back and forth I can see how it flexes. I even have large 12mm thick stainless steel L-shaped reinforcement brackets going from the sides of base and up on the sides of the column but it still flexes. Judging from your picture this IS a weak point in your design as well.

My design is not optimized in any way and I'm sure it could be stiffened up quite a bit if done correctly in the first place but it's not as easy it first sounds. Now, mine IS a CNC-machine so that adds a bit to the cost but I probably could've bought two or three X2's for what I've spent on that machine.

I have to agree with DaraBee, if you want to build a machine as "a project" and learn from it then by all means go ahead but if you want/need a machine in order to do other projects your money is better spent buing one. Heavy cast iron, dovetail slides etc.

Just my €0.02, YMMV.

/Henrik.

[DareBee]

Originally Posted by BuckingFastards How about if I scraped my initial budget and decided to use leadscrews instead of the acme threaded rods? Would this be more precise? Keep in mind I would still like to use the steel rod for the axis to glide on.

Your screws are only the tip of the iceberg from what I am reading/seeing.

A used knee mill is your best value for those travels.

[BuckingFastards]

Well yes my whole purpose is to build a project machine to learn more about the hobby. The fact that I want to CNC it later on will also help me more in this hobby. I just can not afford to CNC it at this point due to finance but will be very happy with just a Manual Vertical Mill in my early stages.

I was rushing when I posted my reply to DareBee and did not read correctly. Rigidity is my limiting factor not precision, so in fact the acme precision threaded rods may be fine? Hmm, what if I did like I see some other builders have done, reinforcing the 8020 with cement. I'm sure that would give the beams a lot more mass, and the concrete should also help to dampen the vibrations. How would this work?

H.O by the way great looking mill you have there.