Initial Design Check Please

[Gotty101]

Hi thanks for the reply

I went with the supported rails due to profile ones being out of my budget

yes they are 1605

i went with that profile as it lined up nicely with the holes in the supported rail, making it easy to join the two.
Sorry i know having no bed and lower frame makes it tricky to check, its just i wanted what i had drawn checking first in case my design is junk.

With regards to mounting the bearing blocks to the gantry sides, do you mean by bolting a plate to the bottom of the gantry side and then the bearings to that, forming like an upside down T shape?

Ok i will make the plate 20mm and remove the rear plate on the gantry. I saw the idea originally on the Sweetdream CNC which did seem like a good idea.

Is there any good reference design on this website i could look at at all?

Thanks again

Trev

[JAZZCNC]

I went with the supported rails due to profile ones being out of my budget

Well if you haven't bought them already this is worth re-thinking. Profiled linear rails from china are now quite cheap and the difference isn't worth not using them.

yes they are 1605

Well this again is worth reconsidering. 5mm pitch is fine for harder materials like aluminium but does restrict the speed for cutting woods and plastics correctly. 10mm is a better balance and while more biased towards softer materials it's still gives more than capable resolution for aluminium.
If you connect to the screws with timing belts, which I suggest you do for resonance reasons, then it's an easy ratio change to increase resolution if you ever find your mostly cutting harder materials which need torque and resolution.

i went with that profile as it lined up nicely with the holes in the supported rail, making it easy to join the two.

Ok ye thought that may be case but layed flat like that weakens the material unless it's well supported from below which could be ok for the base if supported from below but the Gantry has is designed can't be so positioned like that so it will be weak in one direction. I'd think about using square rather than rectangle and beef it up a little, say 80x80 or 90x90, or go with "L" sahpe setup like I've posted on forum many times which is stiff in both directions.

With regards to mounting the bearing blocks to the gantry sides, do you mean by bolting a plate to the bottom of the gantry side and then the bearings to that, forming like an upside down T shape?

Something like this I knocked up to show both screws and gantry but with a little more bracing etc. There's many ways but sat on the bearings is strongest and easier to do.

Ok i will make the plate 20mm and remove the rear plate on the gantry. I saw the idea originally on the Sweetdream CNC which did seem like a good idea.

Argh but he's only used to taking Pics of UFO's and knows nothing about CNC.! . . Lol . . ( He's a mate not being rude.!!)

[Gotty101]

Thank you JazzCNC,

That really cleared things up, expecially with the pictures.

With regards to the profile rails i had a look on ebay and they seemed to get quite $$ when i was looking at the longer lengths, but ive found them on aliexpress and they seem alot better priced and with more options, is this where you get yours from?

i had a look for the Z axis for example and found these rails
http://www.aliexpress.com/item/EGR15...828633643.html
and these blocks
http://www.aliexpress.com/item/1PC-H...044267870.html

Are these the right kind of thing? Only reason im asking is there seems to be different versions ie HGR MGN.

Sorry about all the questions.

Thanks again

Trev

[EddyCurrent]

I would advise against the 15 size, the bearing blocks are an absolute pain to grease, go with 20's all round.

[JAZZCNC]

Are these the right kind of thing? Only reason im asking is there seems to be different versions ie HGR MGN.

Sorry about all the questions.

Hi Trev,

No problem with questions that's why we are here to help each other and ask questions. Don't stop asking questions no mattter how daft they may feel, if your not sure ask.!!

Regards the rails and bearings then like eddy says 20mm tend to be a better size and not just for greasing, they make building the Z axis easier due to being taller and generally give better support with there larger bearings. The rails also sit on the profile better.
With the type then look on the Hi-win site and it will show the difference between the types, it's often very subtle differences like hole centres or bearing heights ratings etc.
Most use the HGH-CA for the slim type and the HGH-CW for the flanged wide type with standard pre-load Z0. If your wondering what pre-load means then it's the amount of pre-tensioning the bearings have when on the rails. Pre-loading removes any slop or play but at same time requires more force to make the bearings slide so we don't want it too high. Z0 is lower pre-load.
Those new to using profiled linear rails are often shocked to find that the bearings don't easily slide when on the rails but require a good shove and then stop quickly. This preload at work. Stand on the buggers and you'll end up on your arse as they work best under pressure and glide like on ice. .. Lol

If your buying from Ali express the look for Fred Lee. Personally I buy ballscrews and rails etc from from Chai at linear motion bearings but he doesn't sell Hi-win brand of rails, they are some other Taiwanese brand which can't think of at minute but they are very good quality do just the same job and a little cheaper.

[Gotty101]

Thanks guys for the help so far. ive scrapped and started from scratch. Ive based it heavily off the pics you posted Jazzcnc, they where a great help and have used 20 Hiwin rails as suggested. Ive done everything in 20mm ali and doubled up on the aluminium profile now. Ive still got a fair bit to draw like the lower frame and bed and stepper mounts with belt drives, and y axis ball screws. Unfortunately im off for a short break so im going to have to go cold turky from solidworks for the next few days.

im going to have to find a good source of 20mm plate next. I was talking to a close family friend about my project who is an ex tool maker so now i have access to his machine shop now which is a great help.

Thanks again all

Trev

[Gotty101]

Hi guys, ive done some work redoing the design as per the suggestions. The lower frame will be made from 50mm square steal box with 3mm wall. The total z axis travel is 120mm. Ive not drawn the bed yet but it will sit in the space at the bottom of the frame but also be adjustable upwards .

Ive still got some things to draw like the z axis screw and stepper ect and x axis stepper mounts.



Trev