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jcb121
26-07-2011, 08:04 PM
In Sketchup I have a kress spindle, I'm trying to work out how high the gantry has to be above the bed.

so with a mill bit installed into a spindle like a kress, how long would the bit showing be?

Jonathan
27-07-2011, 12:22 AM
How long is a piece of string?




Edit: Tempting though that reply was I guess I should be more helpful ... you need to leave enough to change the tool so I'd say about 50mm. The shorter the tool is the better as it will deflect less. Clearly if you put a vice on the bed you'll need more ... this is why I made the height of my bed adjustable (CNC router bed that is!), and made a long Z-axis. Avoid doing the latter though as it's difficult to make it strong enough.

luke11cnc
27-07-2011, 07:17 AM
I would think it is better to have extrusion as your gantry support as you can change or make it a bit longer and just move it up as required ??

I will be leaving a extra 50 mm on the total hight at the bottom of the support rail for this reason

James


even adding two to three more sheets of MDF to the bed would add extra hight if you remove two for a 4 axis ??

Jonathan
27-07-2011, 11:10 AM
I would think it is better to have extrusion as your gantry support as you can change or make it a bit longer and just move it up as required ??

Yes - additionally it allows you to have the minimum distance required for what you're cutting. Clearly that makes it stronger. It's a matter of how difficult it is to actually move the gantry up and down.



even adding two to three more sheets of MDF to the bed would add extra hight if you remove two for a 4 axis ??

Yes it would ... although you'd probably need more height that that for a 4th axis.

luke11cnc
27-07-2011, 11:19 AM
could it be made with a thread adjustment with stops on the gantry supports or just extra deep bed sides with block stops to put bed at different levels

James

Jonathan
27-07-2011, 11:23 AM
If you just have two positions - one low down for sheet material and one high up for whatever, then you can use blocks. Put a block on both sides to rest on for the low position and two blocks that make contact with the top to align it for the high position.

To get it level you can put a DTI in the spindle / z-axis, touching the bed and move the Y-axis. If the bed is not actually flat you'll still need to skim it but that should get it close.

I'm making the height of the bed on my machine adjustible with two jacking screws, and bolts into the 6 supports on the main frame.