alan2525

The cutters are a 4.36mm shank and 140mm in length.

I've attached an image to show one of the cutters, shown with the a brass depth stop on one end and a collet the other, the collet has a grub screw to secure the cutter.


Click on the image above for higher resolution image

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alan2525

It's a desktop engraver / modelling machine, it doesn't have any coolant feed but I've found brushing a drop of water to the cutting area results in no build up of plastic on the cutter.

It's the kind they use to engrave pens, trophies, name labels, brass nameplates on scale model diorama bases etc.

It's far more fun to use it to make tiny parts for scale AFV's though!

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kevingambrell

years ago just after I bought the first CNC we had a job come in that was in delrin. It had three diameters and an off centre hole .005 inch. the three diameters were ok once the tools became dull but the drilling was a real SOB.
In the end we had to have Drill Services make us up a drill special to the job.
plastic can be hard work to machine. Styrene is i know one of the ones people dont like working with.

crash93

First off where do you find the date of posts ? sorry if this is an old thread.
anyway I did some milling of Styrene for a project and it was prob a bit larger than you want but I used Router cutters, the tc ones the likes of Aldi have on offer for about £5 for 20 and it works very well nice neet cuts in 3mm Styrene . I also use a bit of water when drilling Styrene I have a small squeezey bottle of water and as you say it stops the pick up

Attached Images

DSCF0011.JPG (53.4 KB, 19 views)

alan2525

No worries about opening up the thread again - it's good to add some extra info and hopefully it'll help others who have similar technical questions too.

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bogstandard

Hi Alan,
With regards to brazing together a shank and a bit.
I do this fairly often to join drill bits to an extension piece to allow for deeper drilling (I know I should buy long series drills, but when you need them, needs must). I butt join them using silver solder in conjunction with a pair of v blocks and a surface plate, with a small chamfer on the end of each to give a larger surface area for the silver solder to grip onto.

John

radish1us

Hi Alan, a bit late with this post, but here is my version.

About the cheapest way out of this, is for you to go and get a length of 11/64th Silver Steel, this is the Imperial equivalent to the metric size of 4. 36 that you have measured.
You can now use this to make your own cutters.

You cut a bit of 11/64 th Silver steel to the length of 140 mm, then sharpen it as per a normal engraving tool tip, no need to harden it, when it's only playing with polystyrene. Or, if you really need a straight sided cutter, then turn the end down to 1.5 -1.00 or even 0.5 mm x whatever length you need, just sharpen this lot as a "D" bit. If you can't do it, find someone who can, because when the tip looses it's sharp edge, just touch up the cutting edge with a hand stone and away you go again. It aint rocket science were talking about here.

The tip shape should look something like these, have a read, all will be revealed
http://www.majosoft.com/engraving/ht...ened_tools.htm

It is a "D" bit with a pointy end on it, these have been used successfully in this application for decades, so the wheel is not being re-invented here at all.
You should get about half a dozen pieces from a single length of silver steel for a total cost of about 3 or 4 quid, choice is yours.

Here is an E-bay advert for a cutter for the unit you have, check out what shape the cutter is.

http://cgi.ebay.com.au/CarbideCutter...ayphotohosting

This ALL you need for polystyrene, anything else is total overkill and a complete waste of money. The carbide and HSS cutters your using, just DO NOT have the cutting profile to work properly in polystyrene, they are suited for metal removal, not soft plastic.

Have you tried aiming a jet of compressed air at the cutting tip, this instantly clears any bits of plastic and stops it blocking up the cutter, keeps everything cool too.

With the motor spinning at 20,000 RPMS sure makes the tip heat up real quick, if you can slow the revs down, DO IT. If you can't slow it down, then up the feed rate to as fast as it can go, this will slow down the heat exchange to the cutting tip.

Why not try this lot and let the board know how it works.

regards radish

alan2525

I made a few cutters from some silver steel I had laying about. First few test cuts in styrene worked a treat! At 61p for a 13" length of 1/8" diameter, cost of the cutters is peanuts too.

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alan2525

Should the "D Bits" have a relief on both sides of the cutting edge like this?

Attached Images

D Bit JPEG.JPG (4.1 KB, 10 views)

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abrad

Hi All, just thought I would tell you to look on Axminster tool supplies site, they sell second hand tugsten high speed drills and cutters, these are re-ground ex silicon valley cnc bits 50 in a box but it's pot luck what you get.
All is explained on the site. I have used them for years, watch how you take them out of the box some are so small there like needles!!!

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Mind where you squirt that cyno