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Cutting circular holes in plastic

David Smith

By David Smith
in DIY Astronomer

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David Smith

David Smith

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Ok, before we start, if I rated my DIY skills on a scale of 1 to 10 I would get about -5 so bare with me here! :icon_mrgreen:

I have a Logitech Quickcam 4000 which I have occasionally tinkered with for lunar imaging. Had a play with wxastrocapture last weekend and discovered this old webcam works with it :hello2: . I would really like to image some of what I see through my PST (assuming I get to see the sun at some point :rolleyes2: ). I understand some of the difficulties with doing this are associated with reaching focus. So my plan is to remove the main board from the Quickcam and mount it in a small plastic box (similar to a project box, if it works I will purchase something intended for the job). This should result in the sensor being close enough to the aperture of the box to be able to reach focus in the PST.

If at this point you feel I am totally barking up the wrong tree then please let me know :grommit: (I am suffering from starry night withdrawal and I am bored, a dangerous combination!)

With my poor DIY skills in mind I need a means of cutting a 13.5mm circular hole into the plastic housing. I will also then need to do the same to a 35mm film canister (which will serve as the 1.25" adaptor). Initially I thought I could drill the hole, but I do not have a large enough drill bit. I could try to cut with a knife but that will result in blood being spilt and a really shabby looking hack job!

So any suggestions as to how I cut a neat hole in plastic box?

Thanks

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Moonshane

Moonshane

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In principle I agree with Steve - the tool for the job makes life a lot easier.

you can buy cone shaped drill bits which can be used to gradually increase the size of a hole until it's correct. a forstner bit might be a good investment too.

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Avo

Avo

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Have look on ebay, search hole saw.

Various options come up with variable / adjustable one such as this:

http://www.ebay.co.uk/itm/1-New-Hole-Saw-Kit-Adjustable-Metal-2-pc-Circle-Cutter-/140438981558?pt=UK_Home_Garden_PowerTools_SM&hash=item20b2d0cbb6#ht_1300wt_1037

The preferred option is an electricians hole saw kit (Starrett) but that comes at fixed diameters relating to cable sizes etc.

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Bizibilder

Bizibilder

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If you want to drill plastic use a drill bit that is sharpened for wood - See the picture, both these are 10mm bits. The best lubricant I have ever found is good old saliva (Yup - just spit on it!). To start the drill just make a "dent" in the plastic by pushing a suitable point into it. Use slow speed and feed gently, especially when breaking through as this is when the plastic is most likely to split or crack.

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Gina

Gina

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Hmmm, cutting holes in plastic, eh?

The true hacker would melt the hole with his/her soldering iron. :evil:

Ooohh poooh - what's the 'orrible smell!!! :Envy: :Envy: :Envy::eek: :eek:
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Gina

Gina

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Up to 10mm I just use a drill - with great care to avoid splitting. I too have one of those conical bits which is great for opening up holes further or for non-standard sizes. Goes from about 8mm up to 30mm diameter. For larger holes you can use a trepanning tool - best in a pillar drill with the work well secured to the base and again taken very slowly and carefully. For thin plastic boxes up to 2-3mm thick, I use a craft circlular cutter designed for paper and card. Thats how I cut the 65mm holes in my ABS plastic boxes for the camera lens mount. Takes a while but cuts a nice clean hole. If you have the patience for astrophotography, you have the patience for this :D

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pete_l

pete_l

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Don't forget to open the window first!

Hmmm, cutting holes in plastic, eh?

The true hacker would melt the hole with his/her soldering iron. :evil:

Ooohh poooh - what's the 'orrible smell!!! :Envy: :Envy: :Envy::eek: :eek:

The smell will soon disappear, but the hole will remain forever. :grin:

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Bizibilder

Bizibilder

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Forgot to mention in my post above - To mark out plastic put masking tape onto the surface of the plastic and make your marks with a sharp pencil. Never use a scriber as even the slightest scratch is a certain crack starter!

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JamesF

JamesF

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I wasn't aware of the existence of the conical drill bits. I might have to invest in one.

If you want to drill a 13.5mm hole you may find it hard to get a bit in that size. 14mm is more likely. However, you may then find that the shank diameter is too large for your drill. It's not uncommon for lower-powered drills to have a chuck with a maximum shank diameter of 12mm or 12.5mm. Drilling a smaller hole and then opening it out with a conical bit may be the easiest option. A Forstner bit might well work -- it's what I used to cut the hole in the back of the casing of my Xbox cameras when I fitted them with fans. It's not the sort of tool you'd end up using very often though. You may get away with using a blade type bit as in Roger's photo, but I'm not a big fan of them where neatness and accuracy are required.

In any case, support the back of the surface you're drilling with a chunk of scrap timber it at all possible and you'll get a much nicer result. If you can put a piece of timber inside the box and drill from the outside that's obviously better because any rough edges will be on the inside where they won't be seen.

James

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JamesF

JamesF

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You can get shouldered bits where the shank is reduced to 10 or 12mm. I've got a 25mm one.

Indeed you can. And for cutting thin plastic or sheet metal they're probably fine. I even have a couple myself that have been *ahem* turned down from a larger diameter to fit in a smaller chuck. In general though I think they're mostly a good way to kill a small drill that wasn't design for the load, so I try to avoid using them.

James

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JamesF

JamesF

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The reduced shank drills are officially "Blacksmiths drills" in catalogues.

I thought when a blacksmith wanted a hole in something they got it hot and used a hardened point with a hammer :)

James

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JamesF

JamesF

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I have used a soldering iron to adjust the shape of thermoplastic :D I've also used it to weld joins.

Welding plastic seems to be such a common use of soldering irons that I'm surprised you can't get special bits for it :)

James

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