Saturday, July 17, 2010

Primary Assembly done.

My yokes finally came in. As I'd done a lot of the fabrication while waiting 3 weeks for my 'next day' order, it only took me 3 and a half days to assemble it, correct some design errors, and photograph it.

Some changes from the Inventor model below:

I managed to make my Z axis motor work at the back with my (mendel standard) belt length. I moved the vertical assembly forward by 10mm or so to get it right. I also decided not to waste my slider channel and 44x88 extrusion by cutting it short, so I have over 32cm of vertical build volume (after I add a build platform). My X is 30cm and Y is 23.5cm

I'm quite happy with this bearing design.. I can see my 12mm bearing bars flex when I load the axis, but no slop from the bearings at all. It's very slippery. If I change anything, I'll have to get stiffer linear rails first.

In order not to limit my X travel, I had to come up with a narrow belt clamp. Hopefully this will hold, seems like I have quite a bit of clamp pressure. (the ends are just tucked in behind the screws below) My carriage makes it to within a couple mm of each end.

This view, looking up from the bottom. shows my 1:2 timing belt ratio, making my leadscrews turn twice for each rotation of the motor. I've tested the motor with a pololu at half current (ish) and get plenty of Z power, so that's a relief.

This is my Lead-screw nut clamp.. I think it will slide out if (when) I crash my z axis against the bed.. hopefully...

I ended up welding a tab on, rather than remake the part when I discovered the clamp interfered with the X carriage.

I'm not so happy with my Z sliders. There is more movement here than I would like, and they cost a lot, with the guide-rail (30 euros), and sliders (36 euros each).. I can tighten them up some more, but then I'm worried that they'll wear out faster.

I would go with my X and Y bearing arrangement, if I were to do it again, or something more conventional..

Other changes that happened after I started assembly... I drilled through the front of my X carriage and reversed the machine screws so I could adjust the Z slider mounts while they are on the bot... this allowed me to tighten them when everything is lined up. I've also decided not to overdo the countersunk cap screws... I get more adjust-ability by leaving them as regular socket head cap screws.

Otherwise it pretty much matches the model... a good thing I think?

More pictures here:

After much deliberation, I've decided to name it XCbot.

Saturday, July 10, 2010

Primary Fab Done

For the past two weeks, I've been waiting for my RS Components order to arrive. If it weren't for all the required fab work, sitting home by the mailbox would have been a real pain.

Most of the order is here though, and I present about 20 hours cutting and drilling.

Below are some details.

This is my Z axis Slider and X idler pulley

Y bearing bar mounts.
I've counterbored the holes for the bar and idler bearing mounts, more on that later.

Y axis motor mount and idler pulley.

My X and Y slider bearings. I'm using part of a Mendel bearing set.

Detail of how I will constrain off-axis movement. The angle mounts are notched to accept the tension bolts as a tight fit. Side play should be eliminated.
It occured to me to weld, but I have a rotozip bit, and using a jig, this seemed easier.

Detail of the Z slider bearing. It's adjustable so I can eliminate off-axis play.

My conterbored Z drive-screw mount.

The Flexlink yoke mounting system.. I'm just waiting on the 6 x 44mm parts to arrive from a DHL hold, to be ready to assemble.

Tools that I used.

Many people may not be aware that a simple chop-saw with carbide teeth makes a great job of cutting aluminium, if a cutting fluid is used.

If you have multiple parts to drill, take a few minutes to make a jig... It makes a world of difference.

This would have been a 100 euro part If I had ordered it from RS Components. It's the drill jig for the 18mm hole for the yoke hardware. It took me about an hour with angle-grinder, welder and drill-press.

To mount and secure my bearings, I counterbored holes in all holding plates... I accomplished this by using a step-drill for the larger bearings, and this great 12mm drill bit for the 12mm bearing bars. I simply aligned the hole, clamped everything and drilled.