welding steel base or just getting aluminium extrusion

[routercnc]

noob question here with it being the first time tapping a hole my self if the linear rails holes are 4.5mm what would the tap size be to the aluminium plate its attaching to?

If the holes really are 4.5 mm diameter in the rail they are expecting you to use M4 cap head bolts to allow some adjustment. You need a 3.3 mm drill for the pilot drill, followed by an M4 x 0.7 pitch tap (coarse thread).

But I would expect a 25 mm rail to use M6 cap heads? If so these would need a 5mm pilot hole then an M6 x 1 pitch tap (coarse thread).

[reefy86]

If the holes really are 4.5 mm diameter in the rail they are expecting you to use M4 cap head bolts to allow some adjustment. You need a 3.3 mm drill for the pilot drill, followed by an M4 x 0.7 pitch tap (coarse thread).

But I would expect a 25 mm rail to use M6 cap heads? If so these would need a 5mm pilot hole then an M6 x 1 pitch tap (coarse thread).

its 4.5mm on the 15mm rails for the z axis.

thanks again

[routercnc]

OK, then either:
pilot 3.3 mm for an M4 x 0.7 (coarse thread)
pilot 3.5 mm for an M4 x 0.5 (fine thread)

In general I would use coarse thread, especially into aluminium. Get a countersink to clean up the hole and get snug fit of the rail onto the plate - snail countersinks are great.

Also, thread lock (the type you can undo) the screw into the hole as the spindle vibration can undo them.

[reefy86]

thanks mate ill take a look at those

[reefy86]

OK, then either:
pilot 3.3 mm for an M4 x 0.7 (coarse thread)
pilot 3.5 mm for an M4 x 0.5 (fine thread)

In general I would use coarse thread, especially into aluminium. Get a countersink to clean up the hole and get snug fit of the rail onto the plate - snail countersinks are great.

Also, thread lock (the type you can undo) the screw into the hole as the spindle vibration can undo them.

is this what you was talking about for thread lock or is it the stuff in a bottle?
http://www.longlok.com/s.nl/it.A/id.42699/.f

[cropwell]

If the holes really are 4.5 mm diameter in the rail they are expecting you to use M4 cap head bolts to allow some adjustment. You need a 3.3 mm drill for the pilot drill, followed by an M4 x 0.7 pitch tap (coarse thread).

But I would expect a 25 mm rail to use M6 cap heads? If so these would need a 5mm pilot hole then an M6 x 1 pitch tap (coarse thread).

Why a coarse thread ?