There is one thing I'm not to sure about and it's hard to tell from the pics, is that they don't look like the 4 row type bearings.? This makes them that bit less ideal and less able to stand the strain that a Z axis will come under.!! If 2 row type then I think for a Z axis then yes I'd sell them and get 4 row type more suited and making the job a bit easier.!!
Having 4-row profile rails is an advantage over 2-row - twice the balls = twice the surface area in contact with the rails which should get better stiffness, in addition to factors usually mentioned. However 2-row is still in a different league compared to round rails, so unless you can sell them and get better rails for the same price I think there's other places the money would be better spent on. You've got long rails, so use that to your advantage as if you're prepared to sacrifice some travel you can space the bearing blocks out more to reduce the load on each, so long as the piece they are mounted on is stiff. I got 760mm rails for my Z-axis, so if I ever get round to making it I'll keep 400mm travel and have the bearings 360mm between ends, which is slightly extreme but the rails were cheap so why not.
The standard part libraries can be helpful, but I tend to draw things myself so I can be confident it is correct. I guess if I used SketchUp I might think differently.
Regards the profiled rails, I think what I paid for these 'mini slides' was very good and I definitely won't be able to get larger ones for this price. I spent ages today trawling eBay for profile rails and carriages and found that I can get Thk and Nsk sets at similar length for around £150 with p&p. Problem is I had to constantly go to their manufacturer websites and check whether they got 2 or 4 rows of balls. Then you find out the balls also have 30,45, and 90 degree configurations. Plus I started mixing models like hgh, hgw, hsr, ssr, sr, lf, lu with the wrong manufactures.
I've seen Zapp is very reasonable with his Hiwin rails and carriages, which work out at £180 for a brand new set, hgh15ca and 500 rails, compared to £150 for similar spec second hand Thk/Nsk on eBay. I don't understand how there can only be £30 difference, are Hiwin a cheap brand compared to Thk and Nsk.
I'm also not sure what preload is suitable for my z axis, as gravity is always going to pull the carriages down especially when all components are connected to it. Does ZO, little preload, mean there is more play between rail and carriages then ZA, medium preload. I have no actual experience what any type of preload feels like, as I only have the second hand ones to go by, which you can blow from one side to the other.
Personally i would use ZA pre load.
Also a heads up, Hiwin have just raised their prices by about 20%, so expect prices to go up by about 25% with most if not all distributors.Visit Us: www.zappautomation.com
I'm trying to make the build as strong as I can or will ever need. There's no specific need for this router, just for fun. Many of my mates ask, 'what's the first thing you're going to make?' I tell them a plaque saying 'test cut', lol. There's no budget to it, just being wise with money. In the end I'm sure it will cost near £1500 once spindle, plate ali, steel tubing, pulleys and belts are factored in. So far Chai took £550 and Zapp took £250 for the electrics.
Time is always a problem as the family want some dad time in the evenings after work. Suppose I'll have to get my 2 and 4 year olds to help mix up my screws and loose my tools. Funny how all kids love work shops, so many things to play with.
Last edited by Jonathan; 17-07-2012 at 06:22 PM. Reason: Put part in sketchup thread
I'd consider having zero, or very low, pre-load a much bigger issue than only two rows of balls. You've got both...
P.S. Noticed there's two discussions going on here, the machine and sketchup - I can separate them if you want?
I decided to do the version2 upgrade whilst v1 was still in the drawing stage. The main change was to go profile rails on all axis. I also changed the x axis steel rectangle box for 45x90mm ali extrusion as it looks simpler and more accurate to fix the profile rails onto. Same goes for the y axis ali box section except its 45x45mm extrusion. There are two qualities to buy extrusion at, light and heavy. What do most people go with.
Anyways, here are some modified drawings. The first one shows the profile update and the x axis ball nut mount which now allows for adjustment. The middle pic shows how I intend on screwing the bk support block and z motor mount opposite each other. A screw will go from the bk side, through the z rear plate and screw into the motor mount. Hope that is strong enough. Last picture shows how the z plates will be machined to make registers for profile rails and carriages and also allow space for moving parts.
Thanks for looking
Definatly use the 'heavy' extrusion if you can afford it. What profile rails are those and what size...hiwin?
Much more important though is you need some method to tension the belt. The easiest way is to instead of having simple holes in the motor mount, make them slots so you can pull the motor/belt tight then tighten the bolts - again like in the one above. This also allows different pulley sizes to be used without changing the belt, which could come in useful.
Edit: Just to add, moved sketchup discussion here as requested.
Last edited by Jonathan; 17-07-2012 at 06:23 PM.
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