CNC design for consideration

[blackburn mark]

Ok so Chai has replied with a quote. For the 4 rails, 8 blocks, and three machined ball screw assemblies 529usd shipped?!? That seems awfully cheap to me. Does that sound right? I'm about to rip his arm off.

told you it would be silly not giving him a shout :)

only three screws ?? if you are not using two screws on your x axis id have a good think about the implications before you press buy
that extra screw will more than earn its keep!

your design shows four screws? have you already got one for your Z axis?

[John S]

That sounds OK to me, as I said before he's 110% genuine.

[Jonathan]

only three screws ?? if you are not using two screws

Yes! Definitely get 2 for the X axis...
Price sounds about right for Chai. I always pay him directly via a paypal invoice as I think he knocks a bit off due to no eBay fees.

I normally get a quick order from Chi, 7 to 10 days max but the last half dozen orders have generated a VAT plus handling charge from Fedex, usually about £15, not excessive but worth bearing in mind.

Customs recently changed the rules - now everything above £18 value stated on the form gets charged. I don't really mind paying the VAT but £10 handling fee is just extortionate. Last time I just tried paying the VAT (£4.08) and not the handling charge (£10)... so far so good!
Expect to pay another £20 or so since it's a reasonable size order.

[John S]

I don't really mind paying the VAT but £10 handling fee is just extortionate. Last time I just tried paying the VAT (£4.08) and not the handling charge (£10)... so far so good!

If you don't want to pay the £10 then nip down to Heathrow and collect them and pay the VAT there.
Let us know how long it takes you and how much petrol / train fare is

[Jonathan]

If you don't want to pay the £10 then nip down to Heathrow and collect them and pay the VAT there.
Let us know how long it takes you and how much petrol / train fare is

I've already paid for shipping to my door, not Heathrow, so the £10 appears to be to send one letter and collect the money. For the most part it will be an automated system so I don't see how it can cost them £10 to do that - they're clearly trying to make a bit of money. The handling charges used to be much less, and before that they were illegal - I'd happily pay £3-4. Even sending the letter via Royal mail doesn't cost that much!

[John S]

Sorry, didn't realise it was illegal for a company to try to make a bit of money.
You could always collect from Chi

[jonbabbz]

So its all ordered then! Very nice guy. He sent me the standard drawings for the machined ends and I had a peruse to see if they would fit my machine and wouldn't. So I simply emailed him my requirements and he has not charged me anything extra! I will definitely do business with him again. The screws I ordered are just for x and y. i need to redesign the z axis because I'm not sure I want to go with round rail. I think there will be too much deflection at the cutter so ill just buy another smaller ballscrew when I'm ready for it. I want to change the bed too. Here's what I ordered screw wise. I'll create a build log when I get all my parts together. Can't wait :)

[LotusPack]

Hi all,

I just wanted maybe a more experienced builder, to have a look at my design and see if there is anything obvious that might hold my design back before I commit. I posted on cnczone and took all comments on a previous design on board and have now come up with this one. Figured it would be more beneficial to be a member of a UK forum. I am already a CNC owner too so not a complete noob, although it would be naive of me to say I'm not still learning.

The goal was to create it as cheap as possible but try and keep rigidity. I've used 12mm multi-start trapezoidal lead screws on x, y and 10mm on z. Fully supported 16mm rails on x and y and 16mm round rail on z. My main concern is the lead screws on y and the 16mm rail. I used that size because it is easier to implement with the size of aluminium profile I'm using. The machine is 1500mm x 1000mm at the rails, ignore the length of z as im going to shorten it anyway. I designed it with a view to implement a fifth axis at a later date. I will be cutting MDF and PLY only.

Any advise would be greatly appreciated. Thanks

Hi The Y axis looks like it is set on one side; if it is, this will jam as the axis drive needs to be central or with two stepper drives simultaneously operated one on each side of the machine. I would also consider widening the Y axis bearings so the machine has less Y wobble. As you are only cutting MDF and Plywood accuracy is not an isse here that design is good enough. If you can squeese a bit more out of your budget, go for the linier bearings as in the photo.
These are far more accurate and rigid and will increase rigidity and production speed. Keeping this design square in the X & Y plane is going to be dificult.

[mocha]

You could always collect from Chi

Anyone got an address for Chai? PM please. (EDIT: Thanks, got it now)

[jonbabbz]

Hi guys, been really busy lately so updates will be few and far between. Im collecting my parts together at the moment but just wanted to show you a revised y and z axis on my machine and see what you think. Ive moved the rails above and below and gone for supported on z. Ive tried to make z as light and thin as possible so I can get more movement on y. As for the previous design LotusPack, it is driven from both sides you just cant see it because of the angle of the drawing that's all. I considered going for profile rails but I don't want to spend that amount on a first build. Maybe the next one ;)