[tlharris]

After more than a year of lurking, I'm now in a position where I need to buckle down and get my first machine built. Maybe I've over-researched, and have made things out to be more complicated than they need to be.

The objective : build a 3-axis (add 4th later) machine with good enough accuracy and resolution for a small production shop to plow through MDF and acrylic, with perhaps some occasional aluminum sheet thrown on. ON A BUDGET. I'd really like to have a ShopBot PRS Alpha, but was hoping to a machine with that capability for less money.

Basics:
- 48"x96"x12" work envelope
- 3kw chinese H20-cooled spindle
- welded steel frame sides, bolted crossrails. I'll use some of Madvac's epoxy-bedding approach.
- ~100# gantry
- I've no idea WHY, but I set an arbitrary goal of 1000/min rapids and who-knows-what cutting speeds.
- probably headed toward Keling's 906oz-in steppers. Slaved dual-X. Can't decide between R&P and belt drive, but that's another thread.

I've got some mechanical background (engineer, certified welder) just never done much machine design. I normally lean toward extreme overbuilds, but I'm trying to keep myself grounded and focused on the goal at hand : build a machine appropriate for a woodshop, not for NASA. Budget is the primary constraint, followed closely by ease of construction.

So, my basic question here is, I looked into Bishop Wisecarver Dual-Vee, HiWin/THK profile Rails, and Pacific Bearing's IVT rails. Trolled E-bay a lot, and haven't pulled the trigger on anything yet. Anyone able to share thoughts on which direction to head?

Many thanks in advance. I know there's a TON of knowledge here, and looking forward to what folks will share.

[ger21]

So, my basic question here is, I looked into Bishop Wisecarver Dual-Vee, HiWin/THK profile Rails, and Pacific Bearing's IVT rails. Trolled E-bay a lot, and haven't pulled the trigger on anything yet. Anyone able to share thoughts on which direction to head?

I was going to use Dual Vee's on custom made rails for my current machine I'm designing. I made two prototype Z axis (it's a dual spindle design) to see how they worked out. I wasn't very happy with them. they just didn't seem like they'd be rigid enough. Now, I had them mounted to blatic birch plywood, with an aluminum mounting surface epoxied to the plywood. I'm sure they'd be more rigid if mounted to steel.
But I also noticed some axial play in the ones I had (from IMService)

I decided to scrap the prototypes and spend the extra money on legacy HiWin rails and bearings from Automation Overstock, surplus automation equipment, overstock automation devices, manufacturer overruns, linear bearings, variable speed drives, circuit breakers, contactors, starters, relays

Total rail and bearing cost for a 52"x72" machine with 2 Z axis will be about $1300. 2 to 3 times more than the Dual Vee's, but worth it imo.

[tlharris]

Perfect, Gerry... this is EXACTLY the feedback I was hoping for. The BWC's are appealing for on the load capacity & harsh environment fronts, but I don't know that I'd get the accuracy I'd like out of them. Thanks for the link... I'll look into that for HiWin.

I'd love to hear back from anyone who's used the PBC IVT setup. I'm not sure that they'll give the load capacities I'm wanting, but maybe real-life is better than what it reads on the spec sheet.

[RTP_Burnsville]

I have a related question being this thread is about various linear drive systems....

How do the supported, round linear rails compare to the Hiwin/THK style track and car rails?? The style I was thinking of are like those from say Glacern which advertise here on the zone.

My guess is that the THK style support higher loads in a smaller area is all. Any thoughts??

Robert

[olivo]

Hi,
I come from Germany, so my english is naturally not my first choice for discussing machine builds...please excuse mistakes.
Although there is no real question in your thread I just can tell you that my machine is 10x5x1 feet wide and I started also with the idea of doing the x-axis without an undergoing bridge. At first I've to tell you, that my machine is completely made of wood, more exact birch plywood in 18 and 40mm thicknesss. After assembling the two x-axis-gantry-waggons everything looked quite nice and stable. After that I built the gantry bridge (upper bridge). I assembled it on the waggons and I started moving the gantry in the 2 directions...There were much inertia in the parts and I felt really disappointed. My first idea was to make an steel wire/pulley assembly to stabilize the gantry waggons. But then I built up the undergoing gantry bridge an the whole machine was more stable I ever expected. I will drive the gantry with a driven ball screw nut in the middle of my undergoing gantry bridge (ball screw 25mm). Although I will not run the steel wire construction I am sure this would do also an excellent job.

[olivo]

Oh, there is a question: And now my answer. Build your linear bearing by yourself-but do not use alu rails for the most forced parts: better use full supported v2a-rod: supported by wood in my case: It works like a charme...I also made the rail system out of three adjustable parts: SO your your human unexactness is not imporatnd anymore..

[louieatienza]

I have a related question being this thread is about various linear drive systems....

How do the supported, round linear rails compare to the Hiwin/THK style track and car rails?? The style I was thinking of are like those from say Glacern which advertise here on the zone.

My guess is that the THK style support higher loads in a smaller area is all. Any thoughts??

Robert

The Glacern trucks have a static load rating of 300-something pounds each. The THK trucks of the the same width rail can have a static load rating of over 10 times that of the round rail, each! Of course they also cost between 5 and 10 times as much as well.

The ironic thing is, the Glacern rails and other similar styles are probably more tolerant of minute installation inaccuracies, where the profile rails are not.