UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - A 12V DC Variable Speed homebrew PCB circular saw.

David G4EBT · 11th Aug 2019, 5:44 pm

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'

11th Aug 2019, 5:44 pm	#1
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,765	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' Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339. Last edited by David G4EBT; 11th Aug 2019 at 5:52 pm.