The £200 CNC

[Wotsit]

Hi Guys,

I have just started building my router my budget is quite limited, £200 is the figure I am aiming for. I going to be using an open source design from biuldyourcnc.com I thought it would be a good idea to put a log of what I do and use on here.

I'm still wondering what stepper motors and drivers I can get away with, i'm thinking MY103H702 motors with a cheep 24V 1.5A Chinese import multi axis board. My working area is 2'X4'

I had a few hours yesterday up the workshop and this is the sum of my efforts so far

http://www.mycncuk.com/forums/photoplog/index.php?n=52%5B/url%5D
http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Day_One.jpg

Now just waiting for more parts to turn up so I can get on!

[Conan257]

Sounds like a good plan...

I'm also building on a budget, but a little larger as i'm doing it over several months...

Be interested to see your stepper/driver combination as its an issue of contension for me...

[Wotsit]

Did a bit more today, still waiting for my alu angle to arrive from ebay so not that much done.

I got a PC from freecycle the plan was to use it to run the machine but when I picked it up it was only a 486SX.
http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Power_Supply_Case.jpg
It should make a great case for my power supply and driver. I have kept the original power supply because i think I might need 5V at a later date its so old the power supply is linear!

I wanted to use Delrin for my lead screw nuts, but the space is very limited in the Z axis so i put in the middle of the MDF square and bedded it in with a little Epoxy.
http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Z_Axis__Nut.jpg
My M8 "Leadscrews' :heehee: arrived, they were really rough, so i ran a die nut down them an put them over the buffing wheel, made a massive difference, Delrin now spins down freely.

[Wotsit]

My angle arrived today so got a bit done.

Below is the z axis assembled with the x carriage on the back
http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Z_assembled_.jpg
And a close up of the bearings

http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Z_Bearings_.jpg

I am really chuffed about the cleaver bearing design, would buy a beer for the person who had that idea!

I will dowel the MDF that carries the long bearing land for the z to stop it twisting.

Hopefully I will have a a full day at it tomorrow, after I have gone to the local non ferrous metal stockists to get some more angle as I ordered half of what I need.

Sorry for the rubbish photos, only had my phone with me today.

[Wotsit]

Got a bit done over the weekend, this is how it is looking now

http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Todays_Progress.jpg

The table was a great find, 25mm steel box holding the top. I have installed "T" nuts for work holding

http://www.mycncuk.com/forums/photoplog/images/799/medium/1_T_Nuts.jpg

The power supply is taking shape, it only has a 100va transformer in it at the moment which will need to be changed. I also need to fit a bleed resistor to the 10,000uf capacitor as it takes ages to discharge, makes a lovely spark with a screwdriver across its terminals though.

http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Power_supply_test.jpg

I Don't think I am going to be getting my drivers from china, looking for a source in the uk.

[Wotsit]

Slow progress, at the moment. I got some more aluminium angle from my local stockists, paid half the price of the stuff from ebay.

Got the gantry assembled and running over the bed, how tight should movement of each axis be?

http://www.mycncuk.com/forums/photoplog/images/799/medium/1_Current_progress.jpg

I have reinforced the gantry with added MDF just wish i could get the x a bit stiffer.

[Wabbit]

Hi Wotsit,

I'm kind of following you path to a CNC machine as I bought the plans from Patrick at buildyourcnc.com

I have to date - 1 week after plans arrived - failed to make a start.

Still trying to soure basic MDF in the correct sizes to match imperial plans from Patrick in the UK.

3/4 MDF on plans 4' x 2' = B&Q not correct size to start off with ...

We seem to be 18mm MDF only thickness and 3/4" is like 19.nnn

Have I made a big mistake already ??

Guys ??

[irving2008]

Hi Wotsit,

I'm kind of following you path to a CNC machine as I bought the plans from Patrick at buildyourcnc.com

I have to date - 1 week after plans arrived - failed to make a start.

Still trying to soure basic MDF in the correct sizes to match imperial plans from Patrick in the UK.

3/4 MDF on plans 4' x 2' = B&Q not correct size to start off with ...

We seem to be 18mm MDF only thickness and 3/4" is like 19.nnn

Have I made a big mistake already ??

Guys ??

You have to adapt the plans for the different thicknesses. MDF in Europe is 6, 9, 12, 18 or 25mm, while in the US its 1/4", 3/8", 1/2", 3/4" and 1". Its not a big issue; in most cases it makes no difference, in others you have to do a bit of thinking and make an allowance for the difference by adding a mm where appropriate (so for example if you were making a box, you'd need to make two of the sides 2mm longer to get the same external dimensions if that was the critical measurement). The tolerance on MDF isn't that good anyway, its within 0.5mm so the difference between 18mm and 3/4" could be as little as 0.5mm anyway.

[CraftyGeek]

Hi Wotsit,

I'm kind of following you path to a CNC machine as I bought the plans from Patrick at buildyourcnc.com

I have to date - 1 week after plans arrived - failed to make a start.

Still trying to soure basic MDF in the correct sizes to match imperial plans from Patrick in the UK.

3/4 MDF on plans 4' x 2' = B&Q not correct size to start off with ...

We seem to be 18mm MDF only thickness and 3/4" is like 19.nnn

Have I made a big mistake already ??

Guys ??

I'm just finishing the build of the same machine - I've used 18mm.

Start up your own thread & I'll offer you a few of my own findings.

[Wotsit]

Sorry for the long time with no updates but life took over! However I have now ordered some more parts, horray!

SY60STH86-3008BF Nema 23, 1.8 degree hybrid stepper motor with a holding torque of 3Nm (425 Oz-in) £88 from ebay

and

3 Axis TB6560 Stepper Motor Driver £47

As soon as they arrive show my progress

[irving2008]

Sorry for the long time with no updates but life took over! However I have now ordered some more parts, horray!

SY60STH86-3008BF Nema 23, 1.8 degree hybrid stepper motor with a holding torque of 3Nm (425 Oz-in) £88 from ebay

and

3 Axis TB6560 Stepper Motor Driver £47

As soon as they arrive show my progress

What voltage are you going to run that driver on? And what leadscrews have you got?

[Wotsit]

Only 18V with a trapezoidal lead screws, i was going for 8mm bar and derelin nuts but think it might be worth an upgrade. Cost is the major factor for this project, just over the £200 mark now and hopeing to stay there for this one.

[irving2008]

Only 18V with a trapezoidal lead screws, i was going for 8mm bar and derelin nuts but think it might be worth an upgrade. Cost is the major factor for this project, just over the £200 mark now and hopeing to stay there for this one.
18v with that motor/driver combo and 1mm pitch screws will give you a top traverse speed of around 150mm/min assuming direct drive... but then speed and cost are mutually exclusive!

[Wotsit]

Speed is not that important for this project, just trying to use what i have available at the moment. I do also have a 100VA transformer that supplies 34v open circuit but i think that might be to low current and too high voltage for my driver.

Really hope i can cut alu even with a tiny feed in the end.

[irving2008]

Speed is not that important for this project, just trying to use what i have available at the moment. I do also have a 100VA transformer that supplies 34v open circuit but i think that might be to low current and too high voltage for my driver.

Really hope i can cut alu even with a tiny feed in the end.The maximum you can run those boards to is 30 - 32v, and with 3 motors like that you'll need a supply capable of delivering about 10A. Those motors will run at 4.2A bipolar parallel wired for max torque/speed but your drivers will current limit at about 2.5A RMS, 3.5A peak.

Cutting ali is not directly a function of feed rate but a combination of factors includng # of flutes on the cutter, cutter dia, spindle speed, spindle power and the depth of cut (both radially and axially) as well as the feed rate. For a cutter to work efficiently it must actually cut, not rub, so too high a spindle speed combined with too low a feed rate will just wear out cutters and generate a lot of heat without performing much work. If you keep the depth of cut small and can turn the spindle speed down and use a single flute, small dia cutter then you will cut ali.. just anything worthwhile is going to take a long time and you need to consider whether your spindle motor's duty cycle will allow it.

As a rule of thumb the cutting rate for ali is 100m/min and therefore spindle RPM should be 100 x 320/d rpm, where d is cutter dia in mm, so for a 6mm cutter spindle speed you are aiming for 100 x 320/6 = 5333rpm.

Another rule of thumb is that feed rate for ali is around 0.3mm/rev per tooth so with a single flute cutter and a spindle speed of 5000 rpm, you need a feed rate of 5000 * .3 = 1500mm/min which you cant get close to. If you can turn the spindle speed down to 1000rpm say then you are more likely to cut the work than just burn up the cutting tool.

The other consideration is spindle power. Aluminium requires about 17W per cubic centimetre/min. So for a 6mm cutter edge milling a 3mm slot 1mm deep at 100mm/min you need 51W of spindle power at the cutter, or about 100W input. An 80W Proxon or Dremmel wont cut it here... (excuse the pun)