Clamping question

[dudz]

Hi all, haven't been on for a while.

Ok... I'm using the work piece I am doing right now as an example.



The points are for drill holes (4mm x 5mm deep ) to except a bolt.
The material is 6062 T6 ALI. 76x76 x 20mm
I am pocketing around the outside (20mm deep) instead of a profile for less stress on my small machine.

Question is, how do I clamp this without cutting the clamps or without a vacuum bed ?. If I had through holes I guess I could clamp it down with bolts, but I am coming across this issue very often. How do I do it ?

[dudz]

I'm guessing, drill the holes and tap the threads.....Then bolt some spoil board onto the face...clamp the spoil board and machine the part from the opposite side ??

Any better suggestions are welcome

[JAZZCNC]

I'm guessing, drill the holes and tap the threads.....Then bolt some spoil board onto the face...clamp the spoil board and machine the part from the opposite side ??

Any better suggestions are welcome

This will be your best bet.
Unless you have excess material thickness which can be clamped then flipped and surfaced away then it's very difficult.
Really only other way other than sticking it down is to do it in 2 halfs and change clamp position which is a pain.

[dudz]

Ok done it. Its the first piece I have worked on milling more than one side. I am quite chuffed

Not perfect I know. I need to determine how to clean up edges on the machine after profiles.
Its a number plate holder bracket for my Suzuki m/c . Got to make the number plate "backing plate" next that will bolt on the face of this one.

[routercnc]

Glad you solved it - looking nice! Satisfying to make a part to your own design.

As for the finish did you do a roughing pass then a finish pass? Otherwise it might just be the limits of the machine stiffness etc.

As for the bike make sure everything is nice and tight and threadlocked - wouldn't want it dropping into that chain at the wrong moment!!

[dudz]

Thanks
Don't worry, I threadlock everything. Its a V-twin and rattles like a tractor.

I haven't mastered roughing/finishing passes yet. Its just the top edges that get burrs. don't know a quick way of running round the top edge after the profile/pocket has been finished using cambam or if I should use a different endmill to do that.

[routercnc]

I haven't used CamBam for many years but vaguely remember there was a setting to do an offset pass (say +0.5mm) larger than the part. This is the roughing cut. Then pick the actual profile you want and run around again, taking off the last 0.5mm. This is the finishing pass.

I create an offset path in CAD (very quick in AutoCAD) and create the 2 toolpaths accordingly. I don't cut much Aluminium but remember reading that you ideally need to leave a reasonable amount on for the final cut as it can work harden with the roughing pass then the finish pass tries to cut through the hardened part which reduces tool life. You need to cut underneath it (the work hardening is not very deep). I hope someone else can expand on this or put me straight if this is misleading, but that is my understanding.