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cutting the purfling channel
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Greg M
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Joined: 04 Jun 2017
Posts: 12

PostPosted: Tue Oct 17, 2017 10:56 am    Post subject: cutting the purfling channel Reply with quote

Hi everbody. I have finished the top plate of cutting the channel and glueing in the purfling by doing it with a knife and groove cutter. This is my first build it turned out pretty good and had to correct a few mistakes. My question is how much success and quality does the Dremel and attachments work, and if there is other methods I could use to complete this process. thanks
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L P Reedy
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Joined: 02 Apr 2009
Posts: 248
Location: Brevard, NC

PostPosted: Tue Oct 17, 2017 5:57 pm    Post subject: Reply with quote

My experience with Dremels is that very few have good enough bearings to do a reasonable job. The flexible shaft attachments do but have other problems. Much better is a Foredom with an appropriate guide. But any of them require lots of care to prevent extensive damage.
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Rick M
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Joined: 18 Sep 2016
Posts: 24
Location: Okotoks, AB, Canada

PostPosted: Wed Oct 18, 2017 11:24 pm    Post subject: Reply with quote

I'm working on my first as well. I had, I think, pretty good luck with a dremel. I made up an holder/guide (roughly based on StewMac version). I used a spiral cutter and LOTS of trial and error on practice pieces.

A very helpful addition was using a foot control on-off switch, almost impossible (for me anyway) to stop, turn off the switch on the machine and not make a tiny wiggle.

Mainly you have to take your time and let the bit dictate the pace. It's really easy to make a mess in the blink of an eye. And, of course you have to finish the corners by hand.

The spruce was actually a little bit trickier than the maple - softer, more fibrous, maybe ??


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Greg M
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Joined: 04 Jun 2017
Posts: 12

PostPosted: Thu Oct 19, 2017 9:33 am    Post subject: purfling channel Reply with quote

I like your setup it looks pretty good. But how do you lower the cutter head below the top surface to start the groove. Also are you using the 4000 model with the spiral bit. thanks
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Rick M
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Joined: 18 Sep 2016
Posts: 24
Location: Okotoks, AB, Canada

PostPosted: Thu Oct 19, 2017 5:32 pm    Post subject: Reply with quote

The dremel is a model 300. Nothing unique. About 5 or 6 years old because I just haven't used it much. If I was using it a lot I'd likely go with LP's recommendation and go to a Foredom.

The adjustment is partly where the trial and error comes in. I set it by using a gauge block (for lack of a better term) of the thickness that I want to leave under the channel. So if your edge is 4mm, your purfling is 2mm, you'd set it using a 2mm or 2.5mm block. It's kind of a negative way of thinking of setting the height, but does the job.

You do have to watch that tool stays flat - I discovered at least one tough spot that it wanted to climb. It will also try to follow the grain if you don't watch your direction of cut. I learned most of the possible disasters on the test pieces .......

There are a few interesting threads on the forum on this topic.

https://www.violins.ca/forums/viewtopic.php?t=885
https://www.violins.ca/forums/viewtopic.php?t=624
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Greg M
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Joined: 04 Jun 2017
Posts: 12

PostPosted: Fri Oct 20, 2017 9:27 am    Post subject: purfling Reply with quote

Hi Rick. I understand how you adjust the depth of cut with the 2mm. gauge, but if the top/bottom plates move around the flat surface and the cutter is 2mm below the plate , how do you position in the plate under the cutter. Also what did you use to attach the dremel to your wooden jig. thanks
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Rick M
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Joined: 18 Sep 2016
Posts: 24
Location: Okotoks, AB, Canada

PostPosted: Fri Oct 20, 2017 12:58 pm    Post subject: Reply with quote

hmmm....very carefully.......sorry, bad joke, but literally true!! That's where having the foot switch helped a lot. Position the tool above where you want to start, power on and carefully plunge the bit. The top was easier because I used the neck and saddle locations to start and stop.

Attachment. I used a spare dremel collar. Drilled out a bed for it using a variety of forstner bits and then glued in place with epoxy - trying really hard to make sure that it was square/level all around. The StewMac original is machined to thread on to the dremel.

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Michael Darnton
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Joined: 23 Mar 2007
Posts: 1119
Location: Chicago

PostPosted: Sun Oct 22, 2017 11:43 am    Post subject: Reply with quote

Just for reference, here's what I use: http://darntonviolins.com/purfling-machine-eight-views/ You can page through the pix to get an idea of it.

Grizzly.com sells the motor and handpiece quite cheaply: http://www.grizzly.com/products/Flex-Shaft-Grinder/G9928

The handle part started as a 2x2" maple "angle iron" like shape that I made by cutting in from two sides on a table saw to make an L cross section. It took me less than a day to make this, and I've been using it for years.

It's used with the plate hanging over the edge of my bench. The fifth image in this series shows it in use: http://darntonviolins.com/making-a-viola/4/
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L P Reedy
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Joined: 02 Apr 2009
Posts: 248
Location: Brevard, NC

PostPosted: Sun Oct 22, 2017 5:16 pm    Post subject: Reply with quote

Mine is very similar to Michael's (made before I had heard of him), differing in minor details. I use mine to purfle after closing the box.
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Greg M
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Joined: 04 Jun 2017
Posts: 12

PostPosted: Sun Nov 12, 2017 10:30 pm    Post subject: purfling groove Reply with quote

I tried cutting the channel on my drill press , where the top rpm is 3000.
It was going nicely until I broke 2 bits , they were 1/16" hss bits that I got at Lee Valley. Should I have been using carbide bits instead with a 5/64 bit diameter. This is my 1st attempt at doing the back plate and am confused and frustrated on whether to buy a Foredom tool or the dremel with there purfling channel attachment.
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Rick M
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Joined: 18 Sep 2016
Posts: 24
Location: Okotoks, AB, Canada

PostPosted: Mon Nov 13, 2017 12:06 am    Post subject: Reply with quote

Greg, i had a similar episode with the lee valley bit, should have mentioned it earlier. I managed about 2" of a test cut before I broke the first one!

I ended up finding these on amazon

The full description is "SPTA PCB cutters end mill engraving CNC router tool bits 1.4mm For Proxxon Dremel Rotary Tools Pack of 10Pcs". They aren't in stock online right now, but there are loads of other variations on the theme. They were about $30 per package.

Finding anything like this through retail sources in Canada was kind of futile. It may be simpler elsewhere.



I did not try these on the drill press. I made up the other rig while waiting for these bits to ship.

I sympathize on the tool dilemma, I've spent hours mulling choices on the whole range of specialty tools myself. I'm not trying to make a living doing the work, so I tend to pass on the "serious" versions of most things. Having said that, after getting an expensive gouge, I've bought my last cheap chisel!!!
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SioFong Tong
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Joined: 20 May 2017
Posts: 4

PostPosted: Mon Nov 13, 2017 10:49 am    Post subject: Reply with quote

A gewa style single blade cutter works really well. Hold it like a pen and 'writing' on the edge. It is not hard to cut a no mistake purfling grove with it.
But it take time.

I have dictum style and Stewart mac style dremel jig. I feel the Stewart jig works better.

The longer bits are easy to break. I like the bits from cremonatools, short and sharp. The Chinese staff is short too, but not that sharp.
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L P Reedy
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Joined: 02 Apr 2009
Posts: 248
Location: Brevard, NC

PostPosted: Mon Nov 13, 2017 7:57 pm    Post subject: Reply with quote

Years ago I broke several bits like Rick M shows. Then I got a 1.3 mm solid carbide bit from IVC and have never broken it. It finally dulled enough that I ordered a new one. Can't remember when I got the first one but I've probably purfled 30 or 40 fiddles with mostly the older one.
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Greg M
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Joined: 04 Jun 2017
Posts: 12

PostPosted: Wed Nov 15, 2017 5:32 pm    Post subject: Reply with quote

L.P Reedy when you bought those 1.3 carbide bits from IVC were you running them with the Dremel tool with a jig , or did you use some other rotary tool
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L P Reedy
Member


Joined: 02 Apr 2009
Posts: 248
Location: Brevard, NC

PostPosted: Wed Nov 15, 2017 6:06 pm    Post subject: Reply with quote

I use a Foredom because I've never found a Dremel setup that is adequate for my standards. But those bits will work with anything that takes a 1/8 inch shank. One reason they don't break is that they cut well with low side pressure.
Lyle
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