NordicCNC's build log

[NordicCnc]

Can I just ask what the benefit is of using blocks of profile to sit the gantry profile on, as indicated in the picture?



It seems because of this you were forced to place the bottom linear rail on the front, thereby pushing the spindle further away from the gantry. I'd always though that the idea is to try and keep the centre of gravity of the spindle as close as possible to the bearing blocks the gantry rides on.

This is not in anyway meant to be a criticism, but just me trying to understand if this design means there are benefits to it that outweigh the spindle being pushed further outward.

Cheers

Those block are used to increase the gantry clearance. I want to build machine out of aluminium profiles and the 200x80 profile for the Y-axis sides are not high enough. Also by placing the linear rail on the front of the X-axis will allow me to use the work area fully, without increasing the footprint. If I were to put the linear rail on the bottom of the gantry profile I would lose approximately 160mm in the X-axis travel.

You are right about the overhang, but I would claim that it is not that critical. As long as the Z-axis and gantry is stiff enough, it should not be any problem at all. If you check other builds, the overhang is similar!

Thanks for your comment.

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[joe.ninety]

Those block are used to increase the gantry clearance. I want to build machine out of aluminium profiles and the 200x80 profile for the Y-axis sides are not high enough.

Ok, in that context I understand. It's just in most designs I've seen there is simply a gap there... The desired height achieved by where on the gantry sides you bolt the cross-section (the main bit of profile that forms the gantry).
So in your design, the gantry cross section is supported by being both bolted to the side plates and also by sitting on other pieces of extrusion? Are the blocks underneath connected to the cross-section or does the cross-section simply sit atop them?

Cheers

[NordicCnc]

Ok, in that context I understand. It's just in most designs I've seen there is simply a gap there... The desired height achieved by where on the gantry sides you bolt the cross-section (the main bit of profile that forms the gantry).
So in your design, the gantry cross section is supported by being both bolted to the side plates and also by sitting on other pieces of extrusion? Are the blocks underneath connected to the cross-section or does the cross-section simply sit atop them?

Cheers

Yes, L-shape bolted together to the gantry sides. Screw clearance holes in the lower profile, threading into t-nuts in the upper profile. I also intend to use aluminium plates and shim them in the t-slot, to act as guides/stopper so that the gantry profiles doesn't move. The blocks underneath the L-shape also have holes and mounts to the lower profile.

Actually I am extremely glad that you commented on the design. It made me realize that I could further increase the stiffness while not compromising gantry clearance significantly!

I've now removed the 60mm high profiles from the gantry sides. Instead I've replaced the 20mm thick blocks underneath, with 40mm blocks. These are going to be machined so that the Z-axis can pass above the blocks. This effectively decreased height the gantry sides by 40mm, less parts, increase simplicity & accuracy while making the gantry stiffer.



However this means that I need to modify the table to compensate for the lost 40mm clearance.

In the current base frame, I've used 120x80 profiles bolted into the sides, consisting of 200x80 profiles. I have 2 alternatives I think:
1. Replace the 120x80 with 120x60 to gain 20mm clearance. Now I've only lost 20mm clearance.
2. Move the 120x80 underneath the 200x80 profiles (+40mm clearance) and bolt from the bottom. Add 20mm item profiles (wide version) as a "T-slot bed" (+/-0mm clearance).

I think I will go with option 2, which will make the bed stiffer also! The budget allows for it anyway.