[SertanCaki]

Currently I am building a custom 5axis machine for my workshop and I want to locate my leadscrew not in between two linear guides but on top of X axis column. I added two pictures to show what I mean by that sentance. ? would like to know if it is going to cause any problems or not. Thank you.

[peteeng]

Hi Sertan - In a word no. With low friction linear rail systems it does not matter. With high friction systems like bushes or ways, yes it does matter. With high friction systems (or systems with clearance like bushes) the drive has to be through the friction centre of the system otherwise the drive will jam or suffer stick/slip issues. So in your case drive on top is fine. Peter

[SertanCaki]

Peter, thank you for quick reply and advice. I will continue my design this way.

[peteeng]

Hi Sertan - You say you have a leadscrew but I expect your using a ballscrew? I suggest you don't use a leadscrew. Peter

[SertanCaki]

Hi Peter. Yes, I am using ballscrew actually. I am not very good with english terminology, sorry. Does the outcome changes when it is a ballscrew?

[peteeng]

Hi Sertan - the drive position can be the same ballscrew or leadscrew. Ballscrews are very efficient and relatively cheap plus they are more accurate than leadscrews. Leadscrews are cheaper than ballscrews but have more friction and more backlash. Keep at it. I'm designing / building a 5 axis at the moment as well so look forward to your efforts. Do you intend to stress relieve the parts? This is one of the hurdles in building a welded steel machine... Peter

[SertanCaki]

I am planning to weld all the steel beams and then stress relieve the entire assembly. Then the necessery surfaces are going to be machined in a horizontal machine in 1 setup. Then I am planning to fill up the beams with sand to increase weight and help with damping. The weirdly shaped part that is hanging of the x axis guides is a 7075 aluminum framed, epoxy granite filled holder for z axis ram piece. Ram inside is going to be cast iron. I bought syntec 5axis control unit, servo motors and many of the linear and rotary motion equipment. Soon I am planning to share the whole project and get some advice from you guys. I read some of your comments in the forum about frames and damping recently actually, they were helpful, thanks again.

[peteeng]

Hi Sert - I think you will be disappointed with sand filled steel. It will remove acoustic noises but not help overall damping much. Better to use thicker steel, it will be stiffer and if your stiff enough then damping does not matter. Same with 7075, very expensive aluminium then even more expensive epoxy fill. Better to use solid 6061 and it will be much much stiffer and cost less. Its good you have TSR handled that will save you lots of angst. Making the "box" style z axis with internal machine surfaces will be a challenge to get the tolerances right for the cars (if tight the cars will die early) then getting it trammed. Think that through very carefully, maybe a good idea but hard to do in reality. Your bracing uses smaller tube then the main member, this means its on "air" and will deflect a little due to membrane action. It needs something behind it or move it to a side of the member, so it has a wall to push on or use same width tube so the walls agree. Since you are TSR the big weld on the side won't matter... Machine vibrations come from the little things like this, free edges, no shear load path for members etc. Heavy hollows are not a vibration issue. HAAS make very large machines from hollows and they don't fill it with stuff. Concentrate on maxing out rigidity with every part. With TSR you have to make breather holes in everything other wise it will explode or the heat treater will refuse to put it in his oven...

Did you intend welding the 7075? Not advised to do this due to its high zinc content and it will crack...No advantage using 7075 on machines as its modulus is same as 5000, 6000 or alloy of aluminium and stresses are very low. 7075 will corrode on you real fast as well.... Peter

[SertanCaki]

I am planning to use 120x120mm steel tubes with 6mm thich walls. Should I go thicker and forget about sand all together?

[peteeng]

Yes thicker is best & sand is just a problem down the track so leave it out. - Use the thickest tube you can get and this will also give you some machining allowance vs welding a strip to it... Peter