BuildingAfloat

[BikerAfloat]

Hi Jonathan and thank you for your post,

I notice you've opted for steel plate on the Y and Z axis. The vast majority of people use aluminium instead of steel since it is so much easier to machine, particularly with limited/basic tools. 20mm is a good size for the Z-axis.

Opted for 12mm steel for strength and to keep the overhang low-ish (well low within the restrictions of supported rails), I thought I'd keep the aluminium down to a minimum for stiffness. I'll see what the 20mm gains me in reduced overhang, it might be worth a drop in stiffness over 25mm. What size do people tend to go for?

You could make the top Y-axis rail longer (820mm ish?) and increase the spacing of the two SBR25 bearings upon it, so the plate the Z-axis bearings are mounted on would be a T-shape. Although not critical since your Z-axis is already a good size, this would increase the rigidity for little extra cost.

I had considered that, may look at the drawing again, I have to mount limit switches yet and thought the space could take the mountings for them, that was all.

What's the plan for the bed?[/QUOTE]

I am leaving that open in this sketch, but I have plans for several options:

1) A simple MDF bed with 2 layers, support and spoilboard
2) Aluminium (or maybe even steel) drilled and tapped
3) Open to allow a 4th axis to be mounted
4) A removable T Slotted Steel bed across the front cross member
5) Open to allow me to mount motorcycle engine casings on the bench beneath for engraving

Basically I have left it free to see what develops over time.

I'm hoping with the small overall size and the relatively large size of the frame in comparison, it should be up to most of what I can see me throwing at it... Only time will tell.

Cheers,
Geoff.

[Jonathan]

Opted for 12mm steel for strength ... I thought I'd keep the aluminium down to a minimum for stiffness.

20mm thick aluminium would be just as strong. You will save the difference in price between aluminium and steel from the relative machining difficulty.

I'll see what the 20mm gains me in reduced overhang, it might be worth a drop in stiffness over 25mm. What size do people tend to go for?

I think we're talking on cross purposes - I was referring solely to steel plate, not the rails. However since you've mentioned it - the 25mm rails are much better than 20mm since in addition to being a bit stronger due to the size they also have one more row of ball bearings in the blocks.

I had considered that, may look at the drawing again, I have to mount limit switches yet and thought the space could take the mountings for them, that was all.

Having the machine as strong as you can is far more important than having a convenient place for a limit switch. You'll find somewhere to put them.

1) A simple MDF bed with 2 layers, support and spoilboard
2) Aluminium (or maybe even steel) drilled and tapped
3) Open to allow a 4th axis to be mounted
4) A removable T Slotted Steel bed across the front cross member
5) Open to allow me to mount motorcycle engine casings on the bench beneath for engraving

Although clearly 1) is the weakest it's not a bad idea to use MDF to start with as it will be adequate for most things, makes clamping easier and doesn't kill the tool if you make a mistake.

take a look and see if you can spot the mistakes..lol

[...]

Thats better..

Your dimensioning still doesn't add up. Mine is definitely different to that drawing - size, aluminium piece on front is a different shape, smaller connector.

There's also now 4 bearing spindles readily available - these are 215mm long instead of 200mm.

[BikerAfloat]

Hi Jonathan,

Thanks for your post,

"I think we're talking on cross purposes..." - Yup my mistook!

I'm going to have to borrow a mates workshop for this build, so I'll be able to work the steel plate almost as easily as the Ally there, so from a rigidity and space point of view I'm plan to stick with Steel plate.

I wasn't aware of the extra row of bearings in the 25mm bearing blocks, that's a good reason to stick with them, the space saving is only 10mm if I went to 20mm rails on the Z Axis anyway.

Cheers,
Geoff.