A question about drilling into plastic / fiberglass

[Fencer]

I want to hinge my Fastbag lid (the whole top comes off). The base is regular blowmold plastic but the top case portion is a hard plastic or fiberglass. I want to add a piano hinge at the lip and use several small screws.

Question. Is there a particular speed, high or low, I need to use to keep from cracking the shell? The holes are approx 3/16 from the lip. Sugestions on a drill bit. I had planned on a cobalt metal bit with a starter tip.

Thanks

 

[Rickster]

Kevin -- you don't need cobalt, and the pitch may cause a problem if it's 135 instead of regular 118 degree.

I would just use a smaller HSS bit, and slowly open the hole -- step the hole to the size you need.

shouldn't be any problem, and if the bit is sharp, slow will be fine. masking tape on both sides won't hurt either.

 

[twowheelnut]

...and back it with a small scrap of wood to prevent blow-out once the bit penetrates the opposite surface.

 

[ejworthen]

Do not use a regular bit. Get yourself a Unibit. It will not catch on the plastic and crack it. I've used these a lot to drill plastic and they work great. It also beburrs the hole for you. You will be amazed how great these are for drilling plastic. The cheap ones work as good as the expensive ones for plastic.

 

[radman]

+1 on the Unibit.

 

[slapnpop]

Unibit's defiantly the way to go.

 

[Fencer]

And that is why I ask.

Thanks :drinks:

 

[weekend rider]

Oh the uni-bit will not catch? Wrong answer or you may not have never drilled past the increment.

When did metal become softer than plastic, so it will not scratch the plastic?

I question some of the procedures that have been offeered for use.

Lets call this professional differences instead of a knock down drag out I said, he said thing

weekend rider

 

[twowheelnut]

I don't care what you use, just back it... It's like condoms - wrap it or scratch it, your choice.

 

[HondaCBX6]

If you don't have the unibit or Varibit (same thing) and have to use a regular twist drill then use a small twist to make a pilot hole. The use the size that you want and run the drill in reverse. It will melt it's way throgh without cracking the plastic. Let it cool a bit and clean the hole with your finger nail. It works great with no fear of cracking the plastic.

If it is glass then go slow and realize that the drill will be toast after a few holes.

Good Luck

John

 

[Fencer]

Lets call this professional differences weekend rider

And your profession would be?

 

[Knifemaker]

Plastic cracks for two reasons when drilling, One - the speed is too slow, and Two - putting too much

pressure or weight on the piece you are drilling. Plastic is soft and cuts easy, do not press hard down

on the drill/bit.

This would suggest making sure you use a nice new/sharp drill bit, use the highspeed setting , and

watch the bit as it cuts into the plastic to make sure you are cutting and not burning your way through.

As mentioned, back up the piece with wood and if drilling thick plastic, drill in stages rather than all at once,

as the drill will clog and not 'exit' the cut ribbons of plastic.

Thin plastic will crack easy if the speed is too slow ..but most times it's because your in a hurry. Watch the area your drilling and go SLOW.

KM

 

[Rickster]

Kevin -- i don't recall you mentioning what size hole you're wanting to make for the hinge...

another alternative is to use your dremel, and ablate/grind the hole -- but if it's just a weensy (that's smallish) hole -- HSS 118 deg. will be just fine if the hole will be non-weense -- a pilot hole will help ya.

i know you're not drilling into acrylic -- but this may help with bits, speed, methods, issues etc. for drilling into the plastic and fiberglass.

Link

 

[weekend rider]

Now that drilling has an answer. Lets say you are drilling and any of the bits catches and cracks the plastic along the hole you are drilling, now what do you do?

Who makes a plastic repair kit or what kind of glue do you use to repair?

Also what kind of plastic is it like ABS plumbing? Will ABS glue work?

Thanks, I know there is an answer out there some where.

weekend rider

 

[vtcornercarver]

From years of working with blow mold plastic and fiberglass with radio control airplanes, I can tell you that drill bits are NOT the way to go. If you have a dremel tool that came with assorted bits, the carbide cutters, which are shaped like a drill bit but are much smoother and don't catch or tear like a drill, will grind a nice smooth round hole, and you can enlarge it as you need. It doesn't need to be backed up like a drill would, and will never damage a nice fiberglass part. Any hardware store sells dremel bits, and this is a smooth/rounded end carbide bit. good luck Vt

 

[chornbe]

From years of working with blow mold plastic and fiberglass with radio control airplanes, I can tell you that drill bits are NOT the way to go. If you have a dremel tool that came with assorted bits, the carbide cutters, which are shaped like a drill bit but are much smoother and don't catch or tear like a drill, will grind a nice smooth round hole, and you can enlarge it as you need. It doesn't need to be backed up like a drill would, and will never damage a nice fiberglass part. Any hardware store sells dremel bits, and this is a smooth/rounded end carbide bit. good luck Vt

Do you still do that kind of work? I've got some parts I want to tinker with having made.

 

[jestal]

I would also endorse the unibit as the most appropriate way to drill holes in plastic and thin metal. I have drilled a lot of holes with a unibit and have never had it "catch" or splinter the material.

Another alternative that I have also had a lot of success with is a spur point drill as shown in this quick google search article I found https://www.diydata.com/tool/drillbits/dril...s.htm#spurpoint

Taping the surface will help, too, and prevent scratches from the chips or from a slip of the drill bit.

Sometimes a drill bit will want to wander when starting and too much pressure to keep it in position will cause the drill bit to suddenly dig in and splinter the material. Use a thin piece of metal with a like sized hole drilled in it and deburred as a "templete" to hold the bit in position. Lay the piece of stock with the hole in it at the location you want the hole and tape it down to hold it in position. Then drill using the hole in the metal stock as a drill guide or drill bushing. Very easy way to drill holes near the edge of a piece of plastic wihout the drill bit wandering too near the edge.

 

[Fencer]

I just wanted to give a big thank you to the Unibit suggesters. I finally had time to put the hinge to to the lid and have it rivited on. The Unibit worked like a charm.

Thanks again.