What sort of RPM for drilling small holes into plastic? (e.g. HIPS & PE)

Hello

I need to drill extremely small holes (c.1mm, possibly less) into styrene and PE. What RPM should I use?

Background
I am trying to join a piece of HIPS that is c. 3mm by 10mm in cross-section onto a piece of PE. From what I can see, conventional gluing is pretty much out of the question as it will need to be a pretty strong joint.

So I am experimenting with drilling holes using 1 mm drill and then inserting a pin (needle in fact) using a pretty tight fit. I am then cutting off the ends with a high speed rotating disc.

Problem
My problem is that if I use my high speed Proxxon mini drill (Micromot 50/EF) it's minimum rotational speed is too fast (5,000 RPM?) and I keep melting the styrene and this then means that I am taking too much material out of the hole!

My main alternative is to find a clever way to mount the 1mm drill bit in my Black & Decker cordless drill (Hp188F30 which has much slower speeds (quoted at "0-450 / 0-1450 RPM" without load)

OR
I saw this thing in Maplin, which seems to expect you to do the rotational turning for the drills with your fingers?? (WTF?)
"21-Piece Miniature Drill Bit Set with Pin Vice"
**LINK**

I had previously thought that you'd need a really fast RPM to drill using a really small diameter drill bit. Now, because of melting I'm not so sure!
I tried lubricating with water but that seems to make no difference.

Nothing wrong with using a pin chuck or arcamedean drill, done plenty of holes when plastic modeling with them.

This type work well as you can apply pressure to the top piece while rotating the body. I have 4 or 5 of them, keep a different siz ebit in each.

Edited By JasonB on 11/11/2015 20:04:30

Get a mini chuck that fits into your cordless drill chuck. Available from flea-bay, hardware stores.

I use a pin vice along the same lines as Jason.

You might find the plastic doesn't melt if you up the feed rate - sort of punch the drill through rapidly.

John

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Aracmedean drill looks reasonable and would avoid overheating.

I'm less clear about would you pin chuck though...

I tried setting the speed at 5000RPM and doing it v fast. It works a bit. But can then get stuck. Worse, there is no reverse gear in my nice new Proxxon mini drill (Micromot 50/EF) - why didn't any one tell me? So getting it out is rather hard.

Btw, I am toying with chopping the extra pin off the power supply and swapping the terminals around in order to get my reverse gear. Any reason why not to?

Wind it off by hand. Sounds like you fed it too fast.

John

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.

I would advise against trying to reverse it by swapping the DC leads over ... for at least two reasons:

1. the 50/EF has an inbuilt 'electronic speed controller' of unknown [to me] design.
2. if you do succeed in running the motor backwards; the chuck is likely to loosen its grip, with likely unpleasant consequences.

MichaelG.

Edited By Michael Gilligan on 11/11/2015 23:08:22

i would suggest that your drills are 'shot'!

i decent well sharpened drill of that size should not cause any problems, however high the RPM. there are lots of PCB carbide drills of 1mm on the market and ebay and even an ordinary 1mm drill should be ok.

for those of us who do fine work and make injectors 1mm isnt extremely small!

cheers,

julian

Edited By julian atkins on 11/11/2015 23:33:10

In a past life I've drilled tiny holes using disposable syringe needles - just twiddling them in fingers by their hub - they're so sharp that they'll go through living bone with patience (and the odd throwaway) - when I;ve needed to pass fixing wires through small fragments. Smaller than 23g are too flexible wthout great care but 22g or 21g would be easy enough.

OK but nobody is answering the question what is the ideal RPM for drilling 1mm holes into soft plastic e.g. HIPS/styrene.

To get clear part of what is going wrong is that I am trying to drill quite deep holes (up to the full length of the draill bit shaft and although I am raising an lowering the drill a lot, the shavings are getting caught and start generating heat through friction on the walls...

.

John,

This is not meant to be confrontational ... although it will probably appear so:

The reason nobody is answering your question is that there is no simple numerical answer.

The answer will depend upon

• the exact nature of the material you are drilling
• the quality, and style of the drills you are using
• the depth to which you are drilling [still not quantified]
• whether you are working hand-held or with a drill stand.
• etc. etc.

MichaelG.

If you are generating heat, slow the drill way down, say to 100-200 rpm, and pull it back out frequently to clear chips. I would not recommend drilling depth more than 6 to 10 times drill diameter in plastics.

As said before, it sounds like your design is overcomplicated and needs to be simplified to be more easily producible. No one in industry would design something with drilling small holes in styrene to the full length of the drill unless there was absolutely no other way- it is an invitation to trouble, as you are finding out. Same with trying to bond ABS/Styrene and PE/PP.

There are usually ways to redesign things to be simple to make and strong enough to do the job. Styrene and polyethylene are not the optimal choices of material to make machined things with high spring loads. JD

To explain my thinking:

Re "2." I'm not 100% sure of the mechanics, but I think this is unlikely because:
a) Loosening the chuck It's not a problem on my Black & Decker
b) Nor was it a problem with my little Richmond drill
Either way if it's a problem I can soon find out!

On my little Richmond drill I used an old H&M branded controller (originally for model railways I think) that has a dial that you turn one direction for forwards and the other direction for reverse. Works just fine, reversing the direction for the motor without a problem.

I concede that you raise an interesting question about the controller electronics though!

Either way, as a new-comer to all this, I find it jaw-dropping that the long established technology for full-sized drills that builders use (i.e. the ability to reverse) hasn't been used mini-scale drills too.

 

Edited By John Smith 47 on 12/11/2015 11:30:50

Ah fair enough - but I am only looking for an order of magnitude answer.
i.e for a 1mm hole, being drilled in solid styrene which would you recommend?
5000 RPM, 500 RPM, 50 RPM or 5 RPM?

Jeff

Yes, I take your point about it not being something that would go into manufacture. In this case I am purely creating a functional prototype model and I am limited in my choice of materials.

i.e. In the final product it will all be moulded using one material (probably PE). In this functional prototype, I am only needing to redesign PART of the product. The rest of the product stays the same. The part that I am redesigning, I need to build a model out of something that is easy to machine and easy to bond robustly (in this case I have chosen HIPS/styrene).

However, rather than rebuild the *entire* product as a model, much quicker is to simply attach (i.e. mechanically attach) the novel part of the product (which I have made in HIPS/styrene) onto the rest of the existing commercial product (made in PE).

The problem is that in order to test and demo the new product I need pretty good mechanical strength at the junction between the old (PE) and the new (HIPS) part of the product.

And in order to get this strength, given that adhesives onto PE seem so problematic, the obvious answer is to drill long holes and insert metal pins (using a tight interference fit) to give as much strength as possible to the join.

i.e. In order to get the structural strength require I need the pins to be as long as possible...

OK so it sounds like to an order of magnitude as little as 5RPM could be my answer, yes?

For the sort of thing you are trying to do and making some assumptions along that line I think you should look at buying something like this

**LINK**

A lot more flexible than you Proxon and still small and relatively light. It looks like it has a couple of pluses. Depth stop and the ability to tilt one axis of the table - good because you can adjust that axis to be square to the drill, The vice might be junk or on the other hand might not be.

The 16mm chuck is for woodwork really and for the size of drill you are using you will need a pin chuck as per a previous post. The chucks they fit tend to eventually go wonky when small drills are held. On the other hand they often have a 2 morse chuck fitted and that can be changed to say a Jacobs keyed chuck with a capacity of 1/2 / 13mm or less. That size will just hold 1mm drills so a 3/8" or even 1/4 / 5/16 might be wiser just to make sure. The problem with the 5/8 chuck fitted is that there is too much jaw sticking out and not enough inside when they are fitted with fine drills.

There is no real answer to speed. The drill needs to be cutting and producing swarf and not clogging. I'd guess I would try something around 500 rpm or higher with a sharp drill. I wouldn't be at all surprised if the drill took some effort when it was pulled out after drilling the hole especially if it wasn't rotating.

John

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Edited By John W1 on 12/11/2015 13:16:56

Edited By John W1 on 12/11/2015 13:18:42

Ooops!

I have investigated this and I stand corrected. It turns out that MichaelG was correct and that the clutch on modern full-sized hand drill have jaws that do not rotate when you tighten them that their "Keyless metal single sleeve chuck" operate in a fundamentally different way to mini drills.

Moreover it also turns out that in reverse gear the chuck *was* tending to come loose on my old micro drill. And that because they share the same type of clutch that this would be the same problem for my Proxxon mini drill (Micromot 50/EF) as on my old Richmond mini drill.

What I will say is that it didn't bother me much! It was still useful to be able to hit reverse in order to get a stuck drill out - and if it slipped a bit it could be tightened up and hit reverse again!

So on balance I may not chop off that extra pin. But I can't say I'm not tempted...

The point (fortuitous pun) I was making is that a sharp enough implement and slow enough speed to avoid your heat issue. Indeed it may even be easier to use a pin that you drill in and leave rather than drilling a hole and then putting in a pin after struggling to pull the drill out. Say something like a three sided grind (as in toolmakers reamer or bone pin) with a thin smear of slow epoxy into some scratches before placement or even some concentric rings around the pin (yeah hard when this small) so that the plastic grips back into them. It'd take a bit of playing with on some scrap. Dentists also have some tiny screw ended pins for attaching crowns and fillings.