Attaching 'rack' to v-slot

Hey Everyone,
Working on the Z design for my overbuilt CNC machine and I'm wondering if anyone has information on a good way to attach 'rack' to V-slot? Eventually I want to move my entire machine to Rack and Pinion, but I haven't seen anyone do it yet. McMasterCarr sells pre drilled rack, but I was hopping that someone else has already done the R&D.
CNC Mogul is doing it with maker slide but I haven seen any images showing how they attach the rail.

If you haven't seen CNC Mogul yet, check it out. Great design, super clean.

"Joes CNC Evolution" uses a similar design (rack and pinion) for the X and Y. Also nice!

Anyway if you have some info, please share! For now I'll likely just cobble something together so I can start cutting plates, but long term I really like this solution. Super clean and powerful.

thanks
-Sage

Thanks for the info Mark. Do you know where to source rack that would fit in the channel? Not sure how I feel about gluing the rack in... Hopefully someone will come along that has tried it and tell us how it went.

I found a bit more old info here:
http://www.buildlog.net/forum/viewtopic.php?f=31&t=1246&hilit=rack
http://www.buildlog.net/forum/viewtopic.php?f=16&t=1296&start=10
https://plus.google.com/photos/101440406689536737329/albums/5734777303367817569

Thanks guys. I also found this pre-drilled rack on McMaster, Misumi also has some options for a rack that might fit within the extrusion channel, but is way too tall. Clearly it exists since the CNC Mogul guys are using it, but I haven't found anything smaller than the Misumi stuff. I wonder if they are routing out a channel in the extrusion?
http://www.mcmaster.com/#5170t2/=px828u
http://us.misumi-ec.com/vona2/detail/110300429830/?Inch=0&CategorySpec=00000029867%3A%3Aa%0900000029871%3A%3A0.8%0900000029874%3A%3A4%0900000029882%3A%3A301.59%0900000029873%3A%3A120

Regardless, I got my v-slot based torsion box and basic CNC frame up and going. Of course now that I have everything together, I'm considering redesigning it... Using 3/4 inch angle iron to reinforce everything is getting heavy and I'm running out of V-wheels.
-Sage

The CNC Mogul looks very interesting.

I would like to see V-slot have some slide in rack gear option.
Would something like the MiniTec toothed rack 8 slide in and snug up with the set screws it has?

http://www.minitecframing.com/Products/Linear System LR/Catalog_Pages/28.0051_Toothed_Rack_8.html

This would be a great, quick set up option for me.

Thanks,

Excellent Mark

Hey maybe you could extend the face of the solid v-wheel to be a gear to fit in the rack?
Gear drive and guide wheel in one!

I'm keep an eye on the Ox build - looks great.

The wear will be quite significant if the rack is metal and the wheel is delrin but...if the rack is delrin too the wear will be minimal.

BTW, you're right, it's been quite a boon too (see quote).

And Delrin wheels are quite economical to change when they wear.

So here's where I'm at. I'm totally new to CNC but found this site it V-Slot looks amazing. What a great idea!

I want a large portable machine 4' x 4'. Rack and pinion looks to be the best option for me.
CNC Mogul is using rack and pinion but with Makerslide. The rack and pinion on the Mogul looks to be some kind of plastic. (Edit - make that metal) new pics on the CNC Mogul web site.


I'm OK with gluing in, or 3m VHB tape, the rack gear into the slot, but it can't extend up past to where it interferes with the V-slot Delrin guide wheels.

Anybody know of a source for suitable rack gear that is around 5.5 mm width, and less than around 4.3mm in total height to fit into the V-Slot? Pretty much like the CNC Mogul but a little less height?

Thanks!

Here is another source of racks.

http://www.servocity.com/html/gear_racks.html

Check out the site for other parts.

I second that.
Now, if we could use our OX builds to machine toothed v-slot wheel and racks, we could all upgrade to rack+pinion for the price of raw material.

Another:


And another:


Claim:

(updated: all bad rails...) CNCmogul is a trainwreck. Here's what my rails look like: random sized spacers in random positions under pressed in plastic rack. Loads of backlash and binding as pinion travels across high and low spots along rack. Notice how much higher right is than left and neither provide a flat surface for pinion. No amount of pressure will ever seat it properly. No provisions for adjustment of plastic v-wheels to rail or pinion to rack. Tons of resonance coming from all directions, not to mention major deflection at gantry/z-axis, which all ends up where tool meets workpiece. Mine came with junk Chinese controller with counterfeit Toshiba drivers that CNCmogul has refused to replace and I don't see much point in buying another (did get one on amazon, but DOA). Purchased 3 months ago and have been down since day one due to shoddy rails and controller. The new all metal rails look promising, except for hard pinion riding on an aluminum rack. Was promised new machine but it never shipped, I've given up, and am purchasing its replacement from a reputable manufacturer. Lots of successful designs out there with rack and pinion, just expect some noise and vibration. Like CNCmogul mounting the rack under rail or alongside pointed down helps keep debris from surface.

Oh well, CNC Mogul seems to have problems

I still like the idea of a removable gantry on the v-slot.
I've been searching for racks and can't really find anything cost effective.

I have concerns with a belt drive of a rubber band effect. It may not be a real problem, but I'd like a way to minimize it if I use 4ft long rails and it proves to be a problem.

I'm back to looking at a hybrid bulldozer drive using belts. It start with the standard belt and pinion as described on this site but with a full belt loop on top. Use a couple of belt pulleys to guide things.



I'm looking get get some t-nut bar profile which doesn't seem to be too expensive. Maybe something modified a bit with a lower center section, and tap it in a few places.
Put it in the v-slot, tape a GT2 belt on top. It would be like a cheap rack, I think the t-nut bar profile stock would keep things stable.

The top belt would mesh to the t-nut slot belt. The glued down belt would keep the belt from too much tension and stretching, in hopes of keeping the rubber band effect down to a minimum.

As belts wear they could be changed.

If it works, the maybe a modified v-slot extrusion could work. One v-slot could be made shallow so no t-nut bar filler is needed. A belt could be taped directly on the shallow v-slot. This to mesh with a face down belt on top.

If we could purchase 1500 mm V-slot with teeth this would solve the issue.

I smell a new part coming soon.

Then we could use plastic gears, to stop wear & tear.

This one looks almost perfect
Part Number: A 1M12MYHF102000
Flexirack, 1 Module, 2000mm Stock Length, 4mm Face Width. Material- Acetal - Blue.

S=10mm, H1=2mm, H=4.3mm, S3=5mm



take a look at some of the offerings at Stock drive products (Flexirack).. This may not be exactly what you want but it could be neat to try to slide some gear track into the extrusion slot.. It looks like this one will slide right into the existing extrusion and held captive in the V Slot.

http://sdp-si.com/ss/pdf/80501146.pdf