Your thoughts on mill types:

[marx911]

Thoughts on mill type:

Ok I’ve started gathering my pile of stuff to build a mill with so far I have:
4- 41” 20mm THK linear rails
2- 13” 20mm THK linear rails
8- HRS20CR blocks
4- HRS20H blocks
1 – 20x483x5mm ballscrew
1 – Setco 5000 rpm spindle
And some other misc parts.

At this point I still haven’t made up my mind as to whether to build a gantry style or conventional mill style such as the one 5bears built.
What I would like to know is what are the pros and cons in your eyes of the 2 different styles.

My intended use it to build parts for my Harleys. The majority of the parts will be aluminum, but would like to be able to cut mild steel if needed. I also have thoughts to go to a 4 axis machine down the road. I don’t want to post my thoughts on the 2 styles yet so I don’t induce any bias. This will not be a production machine just something I can build parts for my own use. I have a 10x50 Bridgeport clone with DRO and a full size lathe.

Thanks in advance for all answers
Mark

[balsaman]

I think conventional is sturdier, How big a cutting area you want? Will it be cnc?

Eric

[marx911]

CNC yes ....

size... I'm still up in the air I would like 18"-24"x12"-16"x6"-12" xyz with bigger always beings nicer while being aware of falling into the trap of building too big. While at the same time not wanting to finish and think " I could have had a V8" and want just a bit more in travel.

the gantry seems simpler to build larger but most of the ones I see built here are for wood, foam or other soft materials ... while I have seen very large gantry mills in machine shops the are much rarer than the conventional style ... the problem I see with building conventional is the support of the X axis upon the Y axis ... unless you build a pretty wide Y axis base a lot of the X axis becomes free hanging, this is even true in full size mills as the G&L mills we haveat work have outriggers to support the X axis ways when they travel to extream right or left... on a small machine such as the size of the one 5bears built this is not needed because of the stiffness but as you grow in size above that size it becomes harder to make it as stiff.. I guess the machine I'm thinking about would be about twice the size of the one he built.
A gantry on the other hand moves the X axis issue to the Y axis and I'm not sure it can be built stiff enough to mill metal with the same precision...
Mark

[balsaman]

Well,

Even with an over hanging table on a conventional mill, the work is always being done in the center of the y axis base, so the overhanging load is simply the weight of the x axis itself.

I can't see how a gantry can be made rigid enough to cut mild steel, especially one as large as you are talking. Then again perhaps you are a genius....

Eric

[marx911]

Originally Posted by balsaman Well, Even with an over hanging table on a conventional mill, the work is always being done in the center of the y axis base, so the overhanging load is simply the weight of the x axis itself. I can't see how a gantry can be made rigid enough to cut mild steel, especially one as large as you are talking. Then again perhaps you are a genius.... Eric

LMAO I'm glad we had this talk ) I feel better already....
You bring up a good point about the work always being on the center...I will just have to make sure the Y axis base is wide and heavy enough to be able to withstand the offset load
Mark