[Yorch1]

Hello, friends.
You have an amazing forum, I've never seen something like this. Congratulations to everyone!.

Well, I need your expert help. I need an injection plastic benchtop machine ti make my onw hi quality guitar picks (I'm musician).
Where can I find it? (no too expensive, but good quality, please)
What's best plastic to make a 3.0mm hard pick? (resistant)

Thank you all.
Best regards.

[eigendude]

Hi,

I have no direct experience with plastic injection machines, but I have been looking in the topic quite a bit since I saw a demonstration at a local machine show.

The machine that was demonstrated was from this Montreal company:
http://www.abplasticinjectors.com/

From what I recall, the person had to position and clamp the mold in the vise and press a button. Some compressed air was driving the machine and within a second, the machine had finished its injection process. It took a few tens of seconds to let the part cool and extract the demo pieces from the mold manually by pulling on the channels. The demo was making some plastic wheels approx 2cm in diameter and 5 mm thick. The machine seemed well built and very easy to operate.

A few other companies that you could look into:
http://www.minijector.com/products.php
http://www.gluco.com/
http://www.travin.co.uk/tp1.html

The above machines all seem to require that you run a small business around it. It would seem that you need to produce a lot of guitar picks to cover the cost of the machine (5k$-10k$).

The cheapest machine I could find was this one:
http://www.injectionmolder.net/

This link has the plans to make your own that is similar to the one above that you could buy:
http://www.lindsaybks.com/dgjp/djgbk/inject/index.html

I am starting with the CNC milling machine (Taig) and maybe one day will try out an injection molder if I see a need. My background is not in that field, so I am sure an expert will be able to help you more.

Searching the forums of CNC Zone with "Benchtop injection" got me reading some interesting threads on the topic.

Regards,

J-S

[Jeff Davis]

I have no experience with injection molding but I would think that you could mill them from sheet plastic and do a final cleaning with a fine grinder/buffer.

Jeff

[veteq]

Hello Sir,

think that would be a difficult task, pressure in those machines is enormous.
None off the 141163 members made one. think it would be better to mill the parts if possible.

A machine with low pressure wouldn`t make good quality products.

[dertsap]

http://www.pickpunch.com/

[Farasien]

Hi-

I went and bought this book a few weeks ago and have been looking it over since then. Though the plans look simple, there are some part of them that look like they need a once-over to really work well for people like those on this community.

First off, it calls for some fairly difficult-to-get parts. It uses a cartridge heater setup. Finding the right cartridge heater can be difficult- its like having a motor in hand and trying to find a decent controller for it. Now granted, I'm not an electrician or HVAC guy or anything, so I'm not an expert, but knowing what the 'tolerance' (for lack of a better word) is for these, its hard to pick out the right one. It calls for a 250watt cartridge heater that is 3 inches X .625 dia. I've been trolling eBay for more than 2 months now, and have yet to find exactly that. Lots of heaters in higher wattages, many in smaller and the few that hit the 250 watt range are out of the tolerance for size. If I knew if larger wattages were OK, this might not be as big of a problem, but the book gives no range for workable wattages. I suspect higher wattage would be OK, so long as you have a decent thermostat.

...Speaking of which, the thermostat the book recommends is also hard to find. The book has a source or two listed in the back for some of the parts, but none of them seem to be in business. The author also said he was keeping a bunch of each on hand for sale through him to hobby people who buy his book, but they don't seem to be for sale anymore.

Does anyone have any suggestions about any of this? His design seems to be workable- if you can lay hands on the parts, at any rate. I know FigNoggle has a page on his site where he's describing working on an inj. molding machine design, but as of the last entry, it seemed as if it was having some issues with workability.

-Farasien

[Yorch1]

Well I'm not going to build a pplastic injection machine, for sure, but I need to buy one. Do you know where can I get a EMC?

[eigendude]

Hi-

It calls for a 250watt cartridge heater that is 3 inches X .625 dia. I've been trolling eBay for more than 2 months now, and have yet to find exactly that. Lots of heaters in higher wattages, many in smaller and the few that hit the 250 watt range are out of the tolerance for size. If I knew if larger wattages were OK, this might not be as big of a problem, but the book gives no range for workable wattages. I suspect higher wattage would be OK, so long as you have a decent thermostat.

Hi,

In my opinion, a higher wattage heating element would be OK, provided that you have a proper way to avoid temperature overshoots. The thermostat setup becomes quite important. See below.

...Speaking of which, the thermostat the book recommends is also hard to find. The book has a source or two listed in the back for some of the parts, but none of them seem to be in business. The author also said he was keeping a bunch of each on hand for sale through him to hobby people who buy his book, but they don't seem to be for sale anymore.

I haven't checked the book, but from what you describe, its just a thermostat that can act on a remotely sensed temperature. You can build a very decent temperature control system based on a PID controller (http://en.wikipedia.org/wiki/PID_controller). The Wiki link goes into the details of the math, etc., but the main idea of such controllers is very simple to understand. When you are far off the desired temperature, the heater runs at 100% (ON all the time). When you get closer to the desired temperature, the controller reduces the proportion of time the heater is on until it reaches the temperature control point. At the operating point, the controller will have adapted its duty cycle to compensate for the heat losses and the temperature will be kept pretty close to the set point. The PID control offers a much better response than a typical ON/OFF thermostat (those always have to overshoot the set point temperature by the nature of their design).

In order to control a heating element correctly, you need a way to turn it on and off. If the element draws a heavy current, a relay will be required. A solid-state relay has the advantage that it only needs a little bit of current to turn it on/off, thus making it easy to interface to off-the-shelf PID controllers.

To sense the temperature, you can use a thermocouple which is a pretty cheap and simple device.

I'd think that if you can get the heater cartridge with a size close enough to the bore of your heating cylinder, you can machine a sleeve out of aluminum (good heat conductor) and have it all fit together. I would use thermal compound between the heater/sleeve/cylinder to improve the heat transfer. The thermocouple would have to be well fixed close to the point where you want the temperature to be accurately controlled.

To make the complete temp control system, you'd need the following:
- PID Controller
- Type K thermocouple.
- Solid state relay (SSR) that can handle your heater current (add a safety margin). A lot of the SSRs you find will be able to handle 20-40A at line voltages, so its not a problem to control a 250-400W heater.

If you search eBay for something like "PID Temperature Controller", you will find plenty of offerings. Some offer the complete set of PID + Thermocouple + solid state relay, since that would be the typical setup. I think the kit would come to around 40-50$.

In general, once the controller is calibrated properly, the actual power output of your element is not so important. You could use a 250W element or a 500W element, the controller would be able to keep the desired temperature. As long as the whole assembly heats up relatively slowly with respect to the controller's response time, its OK.

This article illustrates the idea with a hot plate:
http://mightyohm.com/blog/2009/01/di...ring-hotplate/

J-S

[KOS]

I have built the Gingery machine as well as I have a small bench top molder as well. The best bet is to just use a punch for that small size of part (most meaning the thickness). You would be better off machining your own punch in whatever shape you want then just punch out your parts.

Farasien, I am probably going to sell off my machine as I do not use it any more. You could probably do some tweaking to mine (as it has been sitting for a few years now) and make it a decent little machine. I did use it with limited success, I was able to machine molds, shoot out some parts that were of quality that were acceptable for my shop but due to the thickness of part I was making there were some sinks in it. Fine for me but not for resale.

[tooManyHobbies]

I had my eye on this one for a while: http://www.injectionmolder.net/

Less than $1500. It'll handle polyethylene, polypropylene, and polystyrene. Don't know what material would work best for guitar picks.

Let us know what route you take!

tom

[Edison4]

Hi,

I was trying to do the same thing! So I purchased this machine:

LNS Technologies High Tech Products for Hobby, Edcucation and Business

And a friend with a CNC machine made me an aluminum mold for a guitar pick.

I tried various plastic materials and eventually had success with Acetal (Delrin™)

Attached are photos of some of my experiments molding plastic parts with that machine.

Hope this helps.

[versotech]

http://www.iasco-tesco.com/ has a few different bench top injection machine in their catalog that seem to be rather affordable however I have never bought from them and can’t vouch for the quality.

[Fastest1]

Hi,

I was trying to do the same thing! So I purchased this machine:

LNS Technologies High Tech Products for Hobby, Edcucation and Business

And a friend with a CNC machine made me an aluminum mold for a guitar pick.

I tried various plastic materials and eventually had success with Acetal (Delrin™)

Attached are photos of some of my experiments molding plastic parts with that machine.

Hope this helps.

That first picture looked like it was printed. It was out of a mold?

[Edison4]

Yes, the guitar picks were made in an aluminum mold using the drill press mounted injection machine from http://www.techkits.com/pim.

A friend with a Tormach CNC mill made the mold for me.

Attached is a photo of the mold

[Psychlist1972]

That first picture looked like it was printed. It was out of a mold?

I noticed that too. Looks like the mold was only roughed and needed either a finishing pass or some hand polishing.

A guitar pick with ridges like that would probably catch on the strings, or snap at those stress lines.

Pete

[Edison4]

Pete,

One thing I've learned while experimenting around with injection molding, is that plastics like acetal and ABS pick up ANY machining marks and reproduce them on the surface of the plastic part.

Interestingly, softer plastic materials like PVC or EVA don't show the machining marks.

I know there are lines that look like ridges in the photos, but they are simply marks left from the CNC machining. If you run your finger over the surface of the mold or the guitar pick, there are no ridges and the surface is actually smooth. It's just a visual effect from the machining.

I guess a mold would need to be polished (like you mentioned) if the parts are showing unwanted visual marks.

[Psychlist1972]

@Edison4

Thanks for the clarification. That makes sense. I know when I do resin casting it picks up *everything*.

The other half of the mold looked like it had no tooling marks, did you polish that, or was it a trick of the light?

[photomankc]

Now that's just cool! An injection mold on my drill-press.

[Edison4]

Pete,

Yes, I did try to remove the machine marks on 1/2 of the mold. But it is still not a nice "mirror" finish. There must be some tricks that professional mold makers use.

[Psychlist1972]

Pete,

Yes, I did try to remove the machine marks on 1/2 of the mold. But it is still not a nice "mirror" finish. There must be some tricks that professional mold makers use.

As I understand it, automotive polishing compound and elbow grease is probably a decent choice for hobby work. Not sure what the pro's use, but likely something equivalent. Also, I'm not sure if aluminum takes the same level of finish as tool steel (one thing injection molds are often made from).

When I've done resin casting in Freeman wax to create masters, I found a light pass with a torch (if detail isn't super fine), or work with an eraser often worked. Worst case, I would take the master/plug and go over it with a thin coat of future floor polish (essentially liquid acrylic) before using it to make a rubber mold. None of those seem applicable here.

Pete