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Old 2nd Mar 2022, 12:50 pm   #1
Nanozeugma
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Default Cutting accurate holes in thin plastic sheet.

Hi all,
I'm in the process of attempting to fashion a replacement drum cover, bearing station names, to replace a damaged original for a Murphy A48.
Thanks to the kind efforts of Jerry (cathoderay57) I now have an accurate reproduction (template) of the station names.
I haven't yet decided whether to use clear PETG sheet with clear self adhesive printed film on the back, or just use OHP film.
Now the problem.
Having marked the hole centres, four per side, where the cover is attached to the metal support frame, I'm struggling working out how to punch the holes accurately (in the right place.)
I have a rotary punch which goes up to 4.5mm, and a standalone 5mm steel punch.
The issue is that I cannot see what I'm doing, trying to align the punch over the proposed hole centres, marked on the material with an indelible marker dot.
I wonder if there is a simple answer to punching the hole(s) in the right place that I may have overlooked?
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Old 2nd Mar 2022, 4:18 pm   #2
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Default Re: Cutting accurate holes in thin plastic sheet.

If you have a hollow punch look down it on an illuminated surface.
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Old 2nd Mar 2022, 6:06 pm   #3
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Default Re: Cutting accurate holes in thin plastic sheet.

I wonder if you can scribe a cross onto the sheet which centres on your 'dot', with carefully-measured arms of equal length just larger than the radius of your wad punch? Then you can ensure your punch is centred by looking for the stubs of those arms protruding equally just beyond its rim, and you know you'll be bang on.
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Old 2nd Mar 2022, 6:34 pm   #4
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Default Re: Cutting accurate holes in thin plastic sheet.

Note sure I understand 100% but can you stick something on top (paper,tape), and draw concentric circles on it?
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Old 2nd Mar 2022, 8:36 pm   #5
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Default Re: Cutting accurate holes in thin plastic sheet.

Yes wireman,
I make very very accurate valve base drilling diagrams that way. Basically I draw a circle and gunsight cross hairs where the hole has to be. I normally use paper but I have printed these onto clear film and stuck them down. I use magictape ( the stuff that doesnt photocopy ) to do so.
I use Librecad as the drawing instrument. My printer is a bog standard Brother multi task machine.

Joe
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Old 2nd Mar 2022, 10:09 pm   #6
SiriusHardware
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Default Re: Cutting accurate holes in thin plastic sheet.

You can buy self adhesive strong paper or plastic 'hole strengtheners' which look like a flat / two dimensional polo mint and are sticky on one side. Their actual function is to reinforce the area around punched holes in paper sheets kept in ring binders.

You could place one, or several, stacked, exactly centred over your intended hole centre and the inner hole will act as a guide to keep the punch in exactly the right place, especially if the outer diameter of the punch is exactly the same as the inner diameter of the circular guide.
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Old 2nd Mar 2022, 11:17 pm   #7
Alistair D
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Default Re: Cutting accurate holes in thin plastic sheet.

After attaching an adhesive label to the material draw horizontal and vertical lines through the centre of the hole you want to punch. When you lay the punch on the surface it is easy to see if it is laying above, below, left or right of the centre.

Al
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Old 3rd Mar 2022, 7:31 am   #8
Electronpusher0
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Default Re: Cutting accurate holes in thin plastic sheet.

I have sucessfully drilled valve base holes in thin(ish) aluminium by clamping it between sheets of plywood.
I printed a drawing of the hole layout at full size I centre popped and drilled the corner mounting holes as accurately as I could.
I drilled the same holes in the plywood sheets and bolted the sandwich together.
I stuck the drilling drawing to the top and drilled pilot holes and finally the large holes using the pillar drill.

Using the ply sandwich prevented distortions of the metal. Should work for thin plastic.

Peter
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Old 3rd Mar 2022, 7:47 am   #9
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Default Re: Cutting accurate holes in thin plastic sheet.

I'm not fully understanding the application, so my suggestion may not be suitable. I use brad point drills to obtain a fine edge when drilling through thin materials.
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Old 3rd Mar 2022, 10:18 am   #10
60 oldjohn
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Default Re: Cutting accurate holes in thin plastic sheet.

Quote:
Originally Posted by SiriusHardware View Post
You can buy self adhesive strong paper or plastic 'hole strengtheners' which look like a flat / two dimensional polo mint and are sticky on one side. Their actual function is to reinforce the area around punched holes in paper sheets kept in ring binders.

You could place one, or several, stacked, exactly centred over your intended hole centre and the inner hole will act as a guide to keep the punch in exactly the right place, especially if the outer diameter of the punch is exactly the same as the inner diameter of the circular guide.
I think this is the way to go, maybe give them a quick rub on a piece of cloth to reduce the stickiness making them easy to remove once the hole has been punched. https://www.ebay.co.uk/itm/132091200...8AAOSwax5YnFwI

The BVWS and other calendars use them on the first page. Not that you could use these, for information only.
John.
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Old 3rd Mar 2022, 9:59 pm   #11
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Default Re: Cutting accurate holes in thin plastic sheet.

Thanks for all the ideas, I'm inclined to think the hole reinforcements idea is the way forward.
I do have some, but they're clear so kinda defeats the object.
Some white vinyl ones on order.
I might just have a dabble with brad point drills on some gash material, if unsuitable, they'll always come in handy for wood
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Old 5th Mar 2022, 11:45 pm   #12
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Default Re: Cutting accurate holes in thin plastic sheet.

Would it help if you heated a sewing needle and made (melted) a small hole in the plastic at the centre of the final hole position?
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Old 6th Mar 2022, 11:34 am   #13
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Default Re: Cutting accurate holes in thin plastic sheet.

Quote:
Originally Posted by Silicon View Post
Would it help if you heated a sewing needle and made (melted) a small hole in the plastic at the centre of the final hole position?
I'd actually contemplated something similar, to whit using a pointy bit on a temperature controlled iron on low heat to make the hole (instead of a punch.) ..... At least, trying the idea out on some off cuts of the material...
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Old 6th Mar 2022, 2:11 pm   #14
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Default Re: Cutting accurate holes in thin plastic sheet.

I have often made holes in plastic with a soldering iron, it leaves a ring behind, once cold this is easily removable with a quick slice with a blade.
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Old 16th Apr 2022, 4:41 am   #15
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Default Re: Cutting accurate holes in thin plastic sheet.

Getting the transparent reinforcing rings in the right place is made easier if you pick up the ring with the tip of a small knife. You can see the whole ring and position it very closely, especially if you have drawn crosshairs through the desired centre.
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