Buying Used Rails

[NerdT1000]

Hi guys,

1st post woohoo!!

Been following everyone's great efforts here for years now and am in the midst's of purchasing for my first machine.

1st problem, buying rails?

I have just spotted some used THK rails and ground screws, 1 Tubaki ground screw too.

I was looking at ordinary Chinese ballscrew and Hiwin linear rails,

For a little bit more I could vastly improve the branding of the components I'd be using but of "used" quality of course.

The components have been pulled from existing machine's so I really need some advice whether it's a good shot.

Instincts tell me NO as they're used, the seller is not listing them as slightly used either which tells me that going with fresh new components off the shelf might be the wiser option.

thanks

[mactec54]

NerdT1000

Used is always a gamble, sometimes they are ok, but most of the time the bearings are quite worn, the rails don't wear so much, so new bearings will take care of them most of the time, So if you buy used don't pay to much

[OBHUR]

Hi, guys ,
my first posting , i wanted to build 4'X 4' cnc router machine for small wood workshop , but a bit confused cause most of the parts like electrical kits and mechanical kits are dame expensive , if any one has trusted chinise supplier will be a great help .
thanks !

[NerdT1000]

Originally Posted by mactec54 NerdT1000 Used is always a gamble, sometimes they are ok, but most of the time the bearings are quite worn, the rails don't wear so much, so new bearings will take care of them most of the time, So if you buy used don't pay to much

Thanks Mac,

[fatal-exception]

Originally Posted by OBHUR Hi, guys , my first posting , i wanted to build 4'X 4' cnc router machine for small wood workshop , but a bit confused cause most of the parts like electrical kits and mechanical kits are dame expensive , if any one has trusted chinise supplier will be a great help . thanks !

Why are you hijacking someone else thread? Is this the first time you've ever been on an internet forum? In case it is, normally you ask your own questions in your own thread.

[OBHUR]

hi, maybe you are in wrong forum all i asked is cheaper supplier for cnc router kit address if you will.
cheers

[Sinistersam]

Keep in mind, used brand name stuff is usually better than new Chinese components. That's been my experience, anyway.

[mchabot]

Really depend on what you are purchasing and for what purpose. If you need exact specifications, nothing else than new will fit. But if you plan to use heavy rail type on a light machine, this will do the trick.

I have purchased some used rails and ballscrew, with more or less success.

For rails, stick to high brand, high performance one, meaning THK HSR (four point rail). Even if they are lightly worn, they will be better than used two point rail or new supported round rail. Never buy rail with one cart on it, pretty useless (except large one for light machine).

Same for ballscrew, be sure to know the exact reference, as some are precision and zero backslash, and other not. I have only purchased NSK FA types, with Z prefix (preloaded), no issues other than slightly lighter preload due to wear. It takes times to have a full set, but this way I know the basic spec of them. I have seen ppl ending paying a lot on ebay for non preloaded ballscrew with low charge capacity.

For the sellers, I had great success with corean ones for linear rails (nearly perfect HSR rails, only one slightly damaged on one cart but working ok). I think these comes from dismantled machineries and not from routine maintenance as they carry a lot of semiconductor machine parts.

For the ballscrew, it was chinese vendors, all ballscrew where ok (but it was for 12/14mm ones, cheaper than 16mm).

I have less good experience with malaysian vendors, cheap but you get what you pay for...

[OBHUR]

Hey,
Thanks, that was really helpful , I was checking with some supplier like HIWI and got quote but as you said it is tricky cause one has to have the right spec and my first plan was to build 4’X4’ cnc router and later on to upgrade it to 4’X8’ . Taking in to consideration the price of Electrical kit and mechanical kits I decided to build the later one ,once for all and I noticed that with regard to the precise motion system parts specially the ball screw and the linear guide rails and blocks has to be prefect . MadVac CNC .com has built heavy and rigid 4’X8’ he has done a good job. I wanted to use the size he used for his router ball screw the following are his method for X, Y, Z respectively.
-45mm Dia, screw type single start, # Turns 2.5X2 Offset types, nut with flange, single nut, tube above nut body and Tread length 2690mm-total length 2918mm length.
-32mm Dia, screw type single start, # Turns 2.5X2 Offset types, nut with flange, single nut, tube above nut body and Tread length 1575mm-total length 1767mm length.
-16mm Dia, screw type single start, # Turns 2.5X2 Offset types, nut with flange, single nut, tube above nut body and Tread length 480mm-total length 555mm length.
Now what type of motor will fit (run it comfortably) the above mentioned spec is my question and I am yet to find out the calculation. but may be MadVac might have used servo motors and if so , the price will shoot up than what I had anticipated because to move 45 mm ball screw may require a machine with a bigger torque . I wonder if you have any idea how to work out on the motor type.