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Old 11th Aug 2019, 5:44 pm   #1
David G4EBT
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Default A 12V DC Variable Speed homebrew PCB circular saw.

In another thread I mentioned that until recently I've used a small diamond wheel electric tile cutter to cut PCB laminate to shape. However, on YouTube, I spotted a little DIY 'circular saw' using a 50mm thin diamond disc of the type used in Dremels and clones. It looked a neat concept but I didn't much like the idea of using telescopic radio aerials for the slides! Here's a link to the video:

https://www.bing.com/videos/search?q...D9A7&FORM=VIRE

6mm 'linear bearings', which are rather like two ball races in one mounting, are widely available and used in 3D printers among other things. They can be bought more expensively in mounting blocks, but I just bought the type that need clamping down and made little aluminium clamps, secured with 6BA nuts and screws. I had some 6mm diameter stainless steel rod, so threaded the ends of two lengths and made two sheet aluminium support plates to which the 6mm rods are fixed. I mounted the bearings on the underside of a 'sled' made from a piece of scrap acrylic sheet.

These are the bearings I used:

https://www.ebay.co.uk/itm/LMxxUU-Li....c100012.m1985

I obtained a small 12V DC 8,000 RPM electric motor with a 3mm shaft onto which I fitted a small chuck into which the shaft of the diamond cutting disc was fixed. The motor is reversible and needs 1.75A. I used a scrap piece of 12mm plywood for the base. As I only make small PCBs, I designed the saw to have a length of travel of 125mm (5") front to back. As a power source I use a 2Amp 12V DC PSU. (I fitted a reverse polarity diode in the ABS box as a precaution).

Motor I used:

https://www.ebay.co.uk/itm/Reversibl...r/322723622152

I bought a PWM motor speed controller, which are quite cheap, and mounted it in an ABS project box sited on the 'sled' about the motor. The external dimensions of the box are 100mm x 68mm x 40mm.

Speed controller:

https://www.ebay.co.uk/itm/Regulatin...72.m2749.l2649

I used 'Nyloc' locking nuts to secure the ends of the 6mm 'rails' to the aluminium end plates.

I guess the two hurdles for anyone who doesn't have a reasonably well equipped workshop would be to thread the 6mm rods, and to cut a slot in the baseboard for the saw blade to run in.

Using a die in a die holder to thread a rod is rather more challenging then using a tap to thread a hole.

The thread cut by the tap will be in line with the hole which guides the tap down into the hole. However, it's quite another thing trying to put a 'true' thread on a rod with a hand-held die holder with the rod clamped in a vice. Threading stainless is also a bit more challenging than mild steel. As I have a woodturning lathe with a large headstock chuck I clamped the die holder in the chuck, then clamped the far end of the 6mm steel rod in a Jacob's chuck in the tailstock. I ground a small taper on the end of the 6mm rod to give the die a good start, then rotated the chuck by hand to cut the thread. The result is a thread that's perfectly perpendicular to the rod.

As to cutting the slot in the base-board, I did that with a plunging router fitted with a 1/8" cutter. I made a rough and ready jig to guide the router and to limit the length of the cut.

As to the performance of the saw, it works fine, but due to the limitations of the chuck and the disc-mounting mandrel, at higher speeds there's some vibration due to dynamic imbalance, but hey - it's an 'MFJ' ('made from junk') PCB saw made in a garden shed - not a gyroscope guiding a spaceship to Mars!

I realise that there's limited interest in homebrew PCB production, and know fine well that I could buy PCBs made to a high commercial standard far beyond what I produce myself, and at less cost, but surreal as it may seem to some, and tedious and time consuming though it may be, it's a facet of my hobby which I enjoy. Yes, designing a PCB, creating the artwork and UV mask, cutting the laminate to size, applying the UY dry film, exposing, developing, etching, drilling, and tinning the PCB, then constructing the project to the best standards I can attain within my skills levels.

That's what I do and that's what gets me out of bed each morning.

A few pics:

1) Underside of motor, linear bearings and 6mm guide shafts.
2) Control box.
3) Top view at end of travel with a PCB cut.
4) Wiring diagram. (The motor is 8,000 RPM - not as shown on the diagram, 1,000 RPM).
5) 6mm stainless steel rod being thread with die holder in lathe headstock.

Hope that's of interest.

'Use what talents you possess,
The woods would be very silent
if the only birds that sang
Were those that sang the best'
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Last edited by David G4EBT; 11th Aug 2019 at 5:52 pm.
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Old 12th Aug 2019, 12:57 am   #2
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Very nice David.

I was looking at 50mm circular saw blades the other day, thinking of doing something similar.

While I no longer make my own pcb's, this type of thing would be ideal for cutting pcb material for making pcb cases (for those of us that are all thumbs in the woodwork dept).
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Old 12th Aug 2019, 12:02 pm   #3
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

VERY Nice David..... Next job....
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Old 12th Aug 2019, 12:56 pm   #4
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

You say the motor takes up to 1.75A- would a 1N5400 series diode be more suitable?
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Old 12th Aug 2019, 2:58 pm   #5
David G4EBT
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Quote:
You say the motor takes up to 1.75A - would a 1N5400 series diode be more suitable?
Thanks for reading the thread guys. Yes, a good point - in fact the IN4007 (being 1 Amp) is probably an impediment. Given that only I will be using it, it's unlikely that I'll connect a reverse polarity PSU to it. I haven't actually measured the current drawn, which might be a good idea - I've only quoted the spec.
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Old 12th Aug 2019, 3:08 pm   #6
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Quote:
Originally Posted by Wendymott View Post
VERY Nice David..... Next job....
I've had a little digital frequency counter module for at least a couple of years that I've done nothing with - one of those cheapo 0.1MHZ - 1.1GHz jobbies. I've now got an ABS box for it and have got as far as creating a front panel to make a water-slide transfer for it, so maybe I'll get on with that. Don't know quite how the counter will perform. I thought it might be a useful project as a low cost accessory for anyone who doesn't have a counter but wants to check the output of their analogue signal generator.

As and when I get on with that, I'll post another thread Wendy.
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Old 13th Aug 2019, 9:51 am   #7
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Haa haa David.... I meant... my next job... already ordered the major parts... mulling over the assembly in my head this am.. in bed..Slide bars and bearings should be here on friday.. Motor and controller a bit longer.
To date i have used my trusty sheet hacksaw to cut pcb material.. it never occurred to me to use a linear slide saw.
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Old 13th Aug 2019, 12:32 pm   #8
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Oh that's good news - I just posted the thread for interest - I hadn't expected that anyone would want to make one!

I forgot to mention a link to the little ABS box that I used to house the speed controller, which is here:

https://www.ebay.co.uk/itm/Waterproo...72.m2749.l2649

Good luck with the project Wendy.
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Old 14th Aug 2019, 10:53 pm   #9
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Thanks David...... I always look at good ideas and decide if its worth the effort... this one certainly did tick the boxes.... Ok about the box... I usually make my own..sheet styrene is in good supply here...
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Old 26th Aug 2019, 2:07 pm   #10
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Hi David and others..... Thanks for the idea....Not Pretty, Dirty but functional. My requirement was for a capacity of 300mm rather than 200mm.. Waiting for the speed controller but not essential.
The linear bearings I found were already mounted...so less metal bashing.
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Last edited by Wendymott; 26th Aug 2019 at 2:08 pm. Reason: Additional info
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Old 1st Sep 2019, 11:32 am   #11
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Hi David.....
Just wondering...what is the depth of your saw cut......mine is about 5mm... thus the sides of the blade are fouling the material and either slowing or even stopping . depending of the speed of the feed.
As I see it.. as the blade has no tooth pitch, thus no clearance sideways,it will grab. I bought a motor from the inscrutable chinese and although reasonably powerful, it stalls.
Two possibilities...
One.. reduce the blade dept so that the tip of the blade just clears the bottom of the material.
Two, slightly skew the blade so its sides are not parallel with the material, thus increasing the gap.

Regards. Wendy
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Old 1st Sep 2019, 2:36 pm   #12
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Reduce the depth of the cut to the minimum necessary - less blade in the material the less drag on it.

Skewing the blade could warp or break the blade.

I would also be inclined to put some sort of cover over the top 3/4 of the blade, if it breaks, you don't want any of it hitting you.
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Old 1st Sep 2019, 3:41 pm   #13
David G4EBT
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Hi Wendy,

I made the slot in the baseboard 7.5mm deep and 3mm wide.

I cut the slot using a router for which I made a jig from scrap wood to limit the length of the slot and to guide the router square to the baseboard. The cutting wheel height is set with a depth of cut of about 3mm it just cuts through the laminate (single-sided FR4 is approx. 1.2mm thick,) so as to reduce the amount of contact of the perimeter of the cutting disc. As you say, too deep a cut means that there is more disdc contact with the laminate and greater 'drag'.

The motor I used has quite high torque. I've checked the revs on an optical tacho and its about 7,500 RPM at full tilt. Really, the speed controller is rather superfluous but I use it to drop the revs a bit because there is a bit of wobble on the cutting disc at full speed, basically due to a slight inaccuracy in getting the chuck to run true. It's secured to the shaft of the motor with two tiny Allen screws and isn't perfectly concentric.

If I go steady, the motor doesn't stall, but if I push it too hard the disc will jam in the laminate and stop the motor so I draw it back to get it back up to speed.

As to the discs Terry, they're the cheap 50mm diam thin metal ones 0.7mm thick, impregnated with industrial diamonds (allegedly!) as used in Dremel style drills. They seem to last quite well and they can shatter, unlike say carborundum discs would do. See pic below.

Hope that helps.
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Old 2nd Sep 2019, 11:50 am   #14
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Default Re: A 12V DC Variable Speed homebrew PCB circular saw.

Hi Terry..... I have a blade cover on it...I will reduce the depth of cut... to "just enough".

The motor I bought is a high speed Toy Car motor so I would have thought the torque was sufficient..

David.. The board channel is deep enough.... it was the depth of cut I was interested in.

I have the same blades as you.

Lets see how it goes.... used it sunday but it was a bit "sticky" as in stalling.
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