[Joezx10r]

Hey everyone I need some help In the design process of building a bench top mill from scratch. I want to built the frame from large heavy wall tubing and plate steel. My ?? is about the linear slides and ball lead screws, how big of a load rating would I need to cut aluminum and light steel work? I want it to be as rigid as possible but not speed a fortune on three sets of slides and screws. Also the steeper motors what would u guys recommended? Thanks.

[SCzEngrgGroup]

Need a lot more information. How big a machine are you talking about? What kind of removal rates are you looking to achieve? What's your budget?

Regards,
Ray L.

[Joezx10r]

Bigger than the cheap import models. Really havnt thought about the removal rates.

[Joezx10r]

Somewhat like the small smithy cnc mill with a little more travel.

[LeeWay]

There are several things you should start with. The first being budget. The second maybe the working enevelope.
Then you will get some more direct info and links. There are many mill builds from scratch on here already. You can check those out for some ideas.
Ebay is full of nice screws and linear slides often. You can get very high quality parts from there for not a lot of cash. You may have to watch many auctions to get just what you want and don't overbid.

There are cheaper solutions you could use if you already have some equipment like a lathe for turning rolled ball screws. You may loose a little accuracy with those, but when double nutted, they become fairly respectable.

[Joezx10r]

The shop I work at lets me build pretty much whatever I want so I have access to a full machine shop and materials at cost. I just think I could build a mill with good quality for the price of the Chinese ones and be better off. Is that a realistic Idea or im I just fooling myself? Its going to be a heavy beast and will be a manual mill till I have the money for motors and controls.

[escott76]

I want to built the frame from large heavy wall tubing and plate steel.

Doesn't matter what you spend on screws and rails if your underlying structure isn't flat and square. Have you given much thought to how to get this type of construction flat and square? How do you plan on attaching parts?
I considered both cold rolled and hot rolled steel sections when designing my mill but I found they would have been more difficult than I wanted to deal with. I additionally had a lot of bar stock aluminum (cut offs) that I wound up using instead, but all things considered I think I would choose the aluminum anyway.
Overall size and spindle power will be determining factors in what you need as far as guide rails and screws. I used 20mm rails and 5/8" screws on mine, but it's small travel wise 9x6x6. The HAAS I work on sometimes uses 25 mm rails, and fairly large screws, and that's a 30x12x16 machine. Decent spindle power on that too. Rigidity isn't just the size of the slide and screw, it's how it's supported, bearing blocks, overall machine structure, separation of rails and blocks from each other. Lots of stuff. Hope you enjoy reading

[LeeWay]

Here is my mill build to start you off. I consider the result between an X3 and a Tormach. The price worked out much lower than the Tormach. It's not nearly as much machine as the Tormach. It is however more machine that the X3 for about the same price as one of those cnc'ed.
It was fun to build as well. Had a blast with it.
http://www.cnczone.com/forums/showthread.php?t=32609

[Joezx10r]

The thought is for a two piece frame. I would build the lower with large square tubing and with wide mounting points machined after welding. Maybe with a Blanchard ground plate or plates for the linear rails to mount to. The column would be similar wide mounts 4 post heavy tube and cross members with linear rails for the head to mount to.

[LeeWay]

I think that you are talking about a bridge mill.
I did initially ponder making mine in that fashion.
There have been a few examples on here I think, IIRC.
After some self deliberation though, I chose the column style. I just set on a pretty simple design. It would seem that a bridge mill would be a little more difficult to get accurate. Not that much more difficult though, especially since you have the bigger machinery at work. I would sure like to see a nice build like that.

If you are planning on using it manually to start with, you will need to include way locks to lock each axis that isn't being moved. Ball screws will back drive very easily in manual mode.

Smaller motors and drives will function, but will limit what you can do with the machine. I would surely save up for a better quality set of motors and drives. Sometimes you can even catch them on sale. My first drive was a Xylotex. They are decent little drives you can save some bucks on, but I found that while they ran my router okay, the mill was just too underpowered to get the kind of production cuts I was wanting. Gecko 201's or 203V's are much much nicer. I bought three 495 oz motors and then a 72 VDC 12 A power supply and now the machine is a little brute.
Good luck with it and I and the rest will help if we can.

I'd like to see a simple drawing of your plan.
Thanks.

[Joezx10r]

Well not really going for a bridge mill but I just seen some pics of a mill build on here that is more what I want and looks really strong. Thanks for the help.

[Joezx10r]

Heres what I got so far, tower plates are 30"x6"x.750 with the rear plate 31.5 long all bolt together and to the 1.50 thick plate that im getting for free.:cheers:

[philbur]

That looks about as stiff as a wet sausage.

Phil

Heres what I got so far, tower plates are 30"x6"x.750 with the rear plate 31.5 long all bolt together and to the 1.50 thick plate that im getting for free.:cheers:

[Joezx10r]

Here is the bottom view of the tower.

[philbur]

Three bolts per side for the column height! It doesn't matter how thick the plates are, the structure is a rigid as the bolts will allow. Weld the column, spread the column base, machine the column, bolt the column to the base.

Just a thought
Phil

Here is the bottom view of the tower.

[Joezx10r]

Three bolts per side for the column height!

No theres going to be more bolts than that I just didnt want to take the time to draw all that in.

[philbur]

A typical bolted joint has 30% of the stiffness of a welded joint.

Phil

No theres going to be more bolts than that I just didnt want to take the time to draw all that in.

[Joezx10r]

[Hirudin]

If you haven't already, check out escott76's build over here. It looks awesome!

Perhaps that plate could be cut into slices to make a much more robust machine.

[escott76]

A typical bolted joint has 30% of the stiffness of a welded joint.

Phil

That may be true, but that looks at stiffness in isolation and does not consider what happens when you melt metal. Even a good welder using proper technique is going to introduce a lot of stress into a structure by welding it. Without a heat treatment cycle to stress relieve and they possibly to bring it back to initial conditions, you are asking for trouble.