View Full Version : Linear bearing compromise

03-31-2004, 06:25 PM
I have descided to go down the road of Shopbot and use these V Groove bearings. They arrived today. At $600 AU, $500 US,
It works out a lot cheaper than buying 9.6M of linear rail and 12
bearings to suit. I guess the trade off is you lose accuracy, but for timber work it wont really matter. Shopbot reports very goood results using this method.

The bearings could come with hardened steel track but I chose to run them on plain old angle iron.

I will report the results.

03-31-2004, 06:52 PM
Ehem.. 12 bearings 500U S$? argh.. ouch.. of what are them built? space grade titanium with ceramic balls of submicron precision diameter?

Well, only joking but I really think that this price hurts..

03-31-2004, 07:00 PM
It beats more than a couple of grand for 9.6M of rail.

Yes I agree that they are overpriced for what they are, I did look around though, and that was the best price I could find. Go on someone post a web site were they are $2 bucks a bearing and I will kill you. :)

03-31-2004, 07:16 PM
Benny I sense heavy anxiety from your postings, seems to me that you take decisions very fast.
Do you get depressed easily?

03-31-2004, 08:48 PM
Konstatin, You are perceptive about the anxiety but not about the depression.

I have the work for the machine before I have the machine. I am friends with this guy who at the moment pays heaps to get his work cut for him on a weekly basis. I have promised him that I can do the same work at a much cheaper cost. It means $1000 per week constantly for me and light work.
At present I make garden orniments out of concrete, now that is back breaking s**t. This is my way out. Not only that, I have other great plans for the machine too.

I see the machine as setting me free to do other things I have dreamed about. While it is cutting I can also work on my other ideas.

It may seem like I make descisions fast, but I have weighed up all the differences over a few weeks. I must eventually make a descision or I will not get things done. My figuing is if I pay too much then so be it, If I make a mistake then so be it. All I can do is make a descision based on what I have learnt and weigh up those choices.

The anxiety is due to my small window of oportunity. If I dont get this done then I will be pouring concrete S**t till the day I die. And that may come sooner if I cant escape from it.

I am applying the philosophy to life "Bite off as much as you can, and chew like buggery" I Know I am out of my depth with the CNC project. 8 weeks ago I had never heard of a CNC machine.
But I will get there.

I suspect you may be thinking about my thread where I said I feel like giving up. Well maybe your right and I do get a little depressed, I would call it discouraged. On the whole I march 2 setps 4ward and one step back.

Sorry to turn this thread into a psych session about me. But your question was an invitation. :)

EDIT: I like to use this forum for more than just getting information. Its like writing a diary, only others can read it and comment on it. I hope by posting my movements, it can either encourage others, or warn them about any pitfalls I take along the way.

EDIT: Oh and thanks for your concern. :)

03-31-2004, 09:42 PM
Your journey is progressing. Keep your eye on the goal, and enjoy the ride, bumps and all. The bearings look good, they should work out well for you. I have not used them myself but the concept looks sound. Oh!, always remember to breath while you chew. Ron

03-31-2004, 10:04 PM
Thanks guys.

Out of interest here is a screen capture from the shopbot pdf assembly guide that shows how the bearings go 2gether. Even with this crude setup they report great results.

Foam, The breathing is real heavy when carrying the concrete around.

03-31-2004, 10:06 PM
Benny I wish you the best.
Good luck on your project.
Keep it up.


03-31-2004, 10:17 PM
Another screen capture from the Shopbot pdf.

It was very nice of them to post the PDF as a free download. I gather they think most will buy thier machine and not build one from their pictures. He he.

Just out of interest. I have all my components for my machine now except for the belts and pulleys. I gave myself a $5000 budget for my 4 X 8 table. I am only $2500 out of pocket so far.
I dont think the belts and pullys will cost the rest. Even though Ive made a few funny choices and purchases, I have found work arounds for them. I think my project is going to be cheaper than I expected.

03-31-2004, 10:25 PM
yneeb- do you have any working machine at this point? have you tried a small one? while gathering aprts, put serious effort into learning a 3dcad application, its worth the trouble! starting small isnt advice only for wussies. i started ultra simple, treaded paths i know people on luberth were doing in 1990.. that was fine. it took 6 or 8 months.. but now i have tried like 10 different linear actuation methods and read thousands of pages of info, and still dont have a decent mill working.

i will soon though.

i must add, like you, i am not really in this for the "CNC hobby" I want to use my machine to devlop product prototypes and help me make robots. im getting sick of waiting for $$ to procced, but all i have is $50-200 at a time.

03-31-2004, 10:40 PM
Yes Vac, good advice for starting simple. The cutting work I will be doing is plain 2D cuts.
And yes learning a 3D cad program is my night time work. I am experiencing a learning curve in many areas at the moment. I feel like my head has swollen with too much undigested information.

You have set me a challenge. I am detemined to get my machine finished in a 3 month span. Hold me to it. You want to know a joke, I already have an order for a machine, and they offered me $15,000 for it.
I just hope these guys dont discover Shopbot in the mean time. Mind you my machine will be a lot more heavy duty than the shopbot one.

Yes developing prototypes and plastic moulds is an area that I want to explore too.

03-31-2004, 11:48 PM
Originally posted by ynneb
Just out of interest. I have all my components for my machine now except for the belts and pulleys. I gave myself a $5000 budget for my 4 X 8 table. I am only $2500 out of pocket so far.
I dont think the belts and pullys will cost the rest.

You're looking less than $500 from PIES depending o what you decide on Benny (thanks for the link btw).

04-01-2004, 12:00 AM
ybenn....I feel a little depsreed!:D

You will be very pleased with the v-bearings. I have used them for 12 yrs and they have never failed me. I don't have a site that sells them for $2.00 but I have 10 of them used that I would sell, no...I still have a use for them! What size bearing did you get?


04-01-2004, 06:01 PM
Turmite, I bought the dual-v wheels and track also. First I tried to mount the track to some mdf, but the mdf just isn't straight enough and the wheels would be tight in one area and slack in another. Should I just give up on mdf and go ahead to mounting the track on metal? Maybe metal from a machine shop who has the tools necessary to make it accurately? How did you mount your track?

04-01-2004, 07:33 PM
I think Turmite you are going to become the Dual V guru.

When you say you have been using them for 12 years, does that mean you have used the one set on your machine for that long, and also does that mean you have run them on mild steel angle iron as the shop bot does? If so, how well does the bearing wear, and how well does the angle iron wear?

Its the unshaped angle iron that I feel a bit iffy about.

If you have run them on the correct hardened steel track, I would also like to hear a report.

I dont suppose you would like to post some current photos of your setup?

Thanks mate.

EDIT: when you say "depsreed" I am assuming you mean depressed, but that doesnt make sense either. What were you meaning?

04-03-2004, 11:14 PM
trent: try acrylic! thick 3/4" or larger stuff is better than MDF.

04-04-2004, 12:34 AM

Isn't the acrylic kind of expensive? Do you have a cheap supplier?

04-04-2004, 08:58 AM
Kind of? Isn't 3/4" acryilc about 20x the cost of mdf?

04-04-2004, 02:28 PM
i dunno - mdf is cheap cuz its cheap.. its not made for building CNC machines. ive been told it warps and has instabilies.. i dunno about that. we use it to build jigs and fixtures for the wood equipment in the school shop - works fine for that...

i get my acrylic as cutoff from a plastics fabricator\distributor.. they are always very friendly and will sell half sheets.. i got a 2'x4' piece of .5" acrylic for $6 last time i was there. if i had wanted a 4x4' sheet, they had one for like $20

you dont have to build the whole machine of acrylic either. just build the parts that need to be most accurate of acrylic. build the parts that dont matter out of MDF.

look for PVC also. acrylic is more rigid, but PVC works easier, and may be cheaper.