Guest WM183 Posted February 7, 2021 Share Posted February 7, 2021 Hi folks. As my scratchbuilding ramps up, I find myself facing a new challenge - how do I cut perfect circles in plastic or brass sheet? is there a circle cutter or something one can use, or do I need to just trace a line with a compass and then try to file and fettle to the line? Spinning in circles, Amanda Link to post Share on other sites More sharing options...
pete_mcfarlane Posted February 7, 2021 Share Posted February 7, 2021 You need an Olfa compass cutter. https://www.amazon.co.uk/Olfa-Compass-Cutter-cutting-circles/dp/B000BK7NWC 1 1 1 1 Link to post Share on other sites More sharing options...
Jeff Smith Posted February 7, 2021 Share Posted February 7, 2021 Interesting that you have to be over 18 to take delivery.......! 1 Link to post Share on other sites More sharing options...
Paul H Vigor Posted February 7, 2021 Share Posted February 7, 2021 8 hours ago, Jeff Smith said: Interesting that you have to be over 18 to take delivery.......! They are worried that you might try sniffing it? Link to post Share on other sites More sharing options...
RMweb Premium PaulCheffus Posted February 7, 2021 RMweb Premium Share Posted February 7, 2021 8 hours ago, Jeff Smith said: Interesting that you have to be over 18 to take delivery.......! Hi It’s a bladed item hence why you need to be over 18. Cheers Paul Link to post Share on other sites More sharing options...
RMweb Premium Compound2632 Posted February 7, 2021 RMweb Premium Share Posted February 7, 2021 10 hours ago, pete_mcfarlane said: You need an Olfa compass cutter. https://www.amazon.co.uk/Olfa-Compass-Cutter-cutting-circles/dp/B000BK7NWC That doesn't look such a convenient tool if the circle to be cut is of small diameter - say below 5 cm. For smaller circles in styrene, I have used a good quality pair of compasses to scribe the curve then snapped along it in the usual way - but still not ideal. Link to post Share on other sites More sharing options...
Jeff Smith Posted February 7, 2021 Share Posted February 7, 2021 No such warnings on bladed items on Amazon over here...... 1 Link to post Share on other sites More sharing options...
RMweb Gold Enterprisingwestern Posted February 8, 2021 RMweb Gold Share Posted February 8, 2021 DSPIAE MT-C https://www.google.com/search?client=firefox-b-d&q=DSPIAE+MT-C Pricey, but you get what you pay for, as with all their products. Mike. 1 Link to post Share on other sites More sharing options...
RMweb Premium Kylestrome Posted February 8, 2021 RMweb Premium Share Posted February 8, 2021 (edited) This is what I use for cutting small holes in paper and thin styrene sheet. A small pair of dividers with one point (uppermost in the photo) stoned to form a sharp blade. It will cut holes from 4mm diameter up to about 80mm. If I have to cut thicker plastic card, I use it to score the outline and then break out the hole in segments. David Edited February 8, 2021 by Kylestrome 1 1 Link to post Share on other sites More sharing options...
RMweb Gold phil_sutters Posted February 8, 2021 RMweb Gold Share Posted February 8, 2021 I don't think that the Olfa would cut any but the thinnest of brass sheet. It is a light-weight plastic job. You need to hold the centre pin steady and gently lead the outer cutter round. Push it too hard and your circle won't stay circular! 3 Link to post Share on other sites More sharing options...
John Harris Posted February 8, 2021 Share Posted February 8, 2021 While excellent for plastic, compasses and the various circle cutters will be useless for brass and are questionable for thicker plastic sheet, the line they make is 'V' shaped, so the hole or disc (whichever you want) still requires fettling to get a nice edge. For brass, I think a fretsaw and patience are the best option, again requiring some attention to get round. jch 1 Link to post Share on other sites More sharing options...
RMweb Premium Compound2632 Posted February 8, 2021 RMweb Premium Share Posted February 8, 2021 28 minutes ago, Kylestrome said: This is what I use for cutting small holes in paper and thin styrene sheet. A small pair of dividers with one point (uppermost in the photo) stoned to form a sharp blade. It will cut holes from 4mm diameter up to about 80mm. If I have to cut thicker plastic card, I use it to score the outline and then break out the hole in segments. David You have illustrated exactly what I was trying to describe. Nicely settable and stays set. Link to post Share on other sites More sharing options...
Guest WM183 Posted February 8, 2021 Share Posted February 8, 2021 Ah, thanks much guys! I have an old Rotring compass someplace, I can give that a go. That circle cutter (the DSP one) looks like a good one to add when the budget permits, as I plan to start building engines too, which have lots of round bits! I'll stick with my fret saw and a good file in brass for now - a lathe will be arriving sometime, but unlikely to be soonish. As much of what I need to cut is smallish (cylinder heads, vacuum cylinder parts, etc) I do need a good cutter. If it's expensive but lasts a lifetime, it isnt so expensive after all. Thank you again! Amanda Link to post Share on other sites More sharing options...
Jeff Smith Posted February 8, 2021 Share Posted February 8, 2021 A possible alternative is to solder the brass parts as much as possible the add circular parts cur from styrene...... Link to post Share on other sites More sharing options...
SP Steve Posted February 8, 2021 Share Posted February 8, 2021 Not sure how small you want to go but the following items may be of some use: https://www.ebay.co.uk/itm/Jewellery-Circular-Round-Disc-Cutter-14-Hole-Punch-Set-Metal-Punching-3-16-mm/252866258025?hash=item3ae000e469:g:hHwAAOSwls5Y8N1H https://toolbug.co.uk/rotary-hole-punch-for-leather-working/ I have the second item and it can quite easily cut through thin brass sheet. When cutting plasticard the cut out pieces tend to stick inside the cutting head but they can easily be prodded through from behind. Link to post Share on other sites More sharing options...
RMweb Premium PaulCheffus Posted February 9, 2021 RMweb Premium Share Posted February 9, 2021 (edited) Hi I use these for small circles they are not cheap though 0.5mm to 2mm in 0.1mm steps https://www.scalemodelshop.co.uk/product/punch-and-die-set-rp-toolz-rp-pd/ 2mm to 4.5mm in 0.2 steps to 4mm then 4.5mm https://www.scalemodelshop.co.uk/product/big-punch-and-die-set-rp-toolz-rp-bpd/ RP Toolz also do hex punches. No connection with the supplier other than as a satisfied customer. Cheers Paul Edited February 9, 2021 by PaulCheffus Clarity Link to post Share on other sites More sharing options...
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