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Home built circle cutter

Posted: Sun Oct 14, 2018 9:44 pm
by Andos
As requested Steve.
I've been thinking for a while it's about time I put something into the forum - I've certainly taken enough out! But I'd didn't think the cutter would've been of much interest as most folks on here are keen on their power tools - and who can blame them - power tools make the job much easier and faster. But for me, this is a way to relax after work. The only power tools I have are a bandsaw and a 8" tablesaw and an ancient old double action, single arm reciprocating bar sander. Everything else is done with blood sweat and cursing.

I made two of these cutters, one to cut radii, the other to scape out the wood between the cuts. This wee beastie is the scraper and it got it's first use last week! It will cut a minimum diameter of 78mm out to a max of 190mm. If I remove the tool height adjuster it will go down to 52mm diameter.
The tool for both is 4.5mm, made from drill bit shanks. Only because I can get them easily
I've given measurements but the only important one is the distance from the base to the centre of cutter bar. It must be 1/2 your bearing diameter.

and dis-assembled
The body
was made from a piece of 2inch brass I've had hanging around for years.
The body shape was made that way because it was easiest and quickest with the tooling I had (it was made "between jobs" at work - so no mucking about!) It was then drilled and tapped M8 about 15mm deep and then bored 20mm by 5 mm deep to take the spigot on the handle. Then parted off allowing enough material to turn the pivot pin.
Remount the body in the lathe so you can turn the pivot pin (dia 8mm by 20mm long) and counterbore the base deep enough to give the bush a bit of clearance. I went in 3.5mm at 25mm dia.

To drill the holes for the radius bar, adjuster and clamp I used a dividing head mounted in a mill but there is no reason, with a bit of care, that they can't be machined in a drill press. the only important measurement is the distance from the base to the center of the radius bar. It must be 1/2 the diameter of the bearing that will be mounted on the end of the bar. The adjuster and clamp I drilled and tapped M6

The Radius bar

10mm diameter (stainless steel bar) by far to long for what is required. I'll cut it off at the second groove one day which will leave it 190mm long.
First I mounted it in a vice on the mill and machined the flat. Starting 25mm in from the bearing end and making it 95mm long and wide enough to take the 6mm diameter clamp screw.
After machining the flat (or filing it if you don't have a mill) turn it 90 degrees in the vice and clamp it back up with a piece of key steel against the flat. This will hold the bar in the correct position for the next operation.

The tool mounting and adjuster holes
Drill the hole for the tool far enough in from the end to allow room for the bearing then drill and tap the hole for the tool height adjuster about 8mm further in. This measurement will vary depending on the tool and adjuster diameters. I used 4.5 and M5 with 3mm clearance between them ( yea I know the maths don't add up but it's not a critical measurement)
Now back to the lathe - turn the end down to 9mm for the bearing (9 x 24 x 7wide) drill and tap M5 for the tool clamp.
Reposition the bar in the chuck jaws to machine the slot for the adjuster. 130mm in from the bearing. Use your parting tool to machine a groove 2.5 to 3mm deep.

That's the 2 major components.
all the wee clamps and adjusters I'll post tomorrow

Re: Home built circle cutter

Posted: Mon Oct 15, 2018 5:28 am
by GregL
Hi Andos,

Very interesting! You certainly put your metal-working skills and experience to good use (not to mention the metal-working machinery!)
If possible, could you please include pics of your cutter tool and scraper tool in your next installment. I have a circle cutter and scraper made long ago by user Localele - that is similar in concept - and I'm interested to see how you shape your cutting and shaping tools, and what shape they are.


Re: Home built circle cutter

Posted: Tue Oct 16, 2018 10:43 am
by simso


Re: Home built circle cutter

Posted: Tue Oct 16, 2018 3:51 pm
by lamanoditrento
simso wrote:
Tue Oct 16, 2018 10:43 am


Re: Home built circle cutter

Posted: Tue Oct 16, 2018 9:22 pm
by Andos
Thanks Steve, Trent,
This is not as easy as I first thought - not quite sure what level I should pitch it at. It gives me a lot more respect for the efforts you put into your tutorials Steve.

Greg I haven't forgotten you. Your question on the cutting tips has lead me down tracks I'd never considered before. I'll get back to the cutters this weekend.

and now for part 2

The tool clamp and adjuster bits

and the radius arm clamp and adjuster
Thee are pretty much the same except that the tool parts are all M5 threads and the radius arm parts are M6 threads
The knobs are made out of 1/2" brass bar, knurled, tapped and parted off about 1/2 long.
The adjusters are machined from 20mm stainless bar, with the radius adjuster machined to have 0.05m clearance to fit the slot machined earlier in the arm.

the handle
The centre screw is an 8mm setscrew with the hex turned off and a hacksaw slot for a screwdriver
The handle came from some firewood the misses bought. I have no idea what it is except that it is bloody hard!

Almost forgot the bush
A 16mm cap screw. It has a 16mm sholder machined into the base of the head, then turn the hex off and finally drill and ream an 8mm hole up the middle. The thickness of the head should be 0.5mm smaller than the recess machined into the base of the body.

Here's a few pics of the various assemblies
and in action
The top is mangeao
I want to put a herringbone in next and then I'm not sure what but a few more layers and finish the rosette with another BWB. I'm struggling with making the herringbone - 3rd time lucky - I hope!

Re: Home built circle cutter

Posted: Sat Oct 20, 2018 2:40 pm
by simso
Yes tutes take some time, and many times I will photo a tute and then when I collate the lot, have missing important photos, so I will scrap the tute all together and hopefully do it again one day

Impressed with your fabrication skills there


Re: Home built circle cutter

Posted: Sun Oct 21, 2018 2:49 pm
by Andos
Here's those cutting tools
The one on the right is magic in both directions to about 2.5 or a little deeper. Flat on the face, 3mm to the back shoulder and tapers on the back from the tip to 1mm at the shoulder. Good for cutting rosettes but not so good for going full depth on a sound hole.

The scraper on the left is 2.2mm across the face. It tends to dig in cutting into the grain. It's going to get a wee bit of negative rack on the face and back clearance angle reduced a little to try and counter the digging in.

Here's it's latest result
This is my 4th rosette.
It's taken 8 attempts and 3 weeks to get this far
2 goes to get a decent block which promptly got wasted on learning how to cut, clamp and plane it to size.
This is the 3rd. I glue paper to the sides to help hold everything togeather.
another 2 goes at getting the herringbone into the rosette cut out.
Frustration started to get the better of me so I thought it best to stop at this one.
The biggest disappointment is the mess at the top ends - that is just plain sloppiness .

Re: Home built circle cutter

Posted: Sun Oct 21, 2018 2:51 pm
by Andos
Sorry some of those pics are a little out of order, but you'll work them out :mrgreen:

Re: Home built circle cutter

Posted: Mon Oct 22, 2018 3:12 pm
by Andos
If you like my fab skills you'll be impressed by these 2 :lol: :lol:
I needed a 42mm soundhole cutter in a hurry

and for the ultimate in purfling and binding routers
just add 1 chisel!!
Its a piece of 3/16 tool steel in a 4.5mm hole to give a bit of grip. Tap in for the depth of cut then press lightly and take your time - or else it'll pull out cutting into the grain.

I managed this with it
but it's definitely going to get sexied up before it's next use

Re: Home built circle cutter

Posted: Wed Feb 27, 2019 10:01 am
by Petecane
The first all metal one is a work of art and beyond me as I have no metal work lathe.
Splendid job.
I also liked the two KISS tools.
I am an advocate of keeping it as simple as possible.
I have just yesterday, finished making a couple of sound hole cutters which I would like to post and describe but do I do it on this thread or open another one?
Makes sense to do it here but I don't want to hi jack someones thread.
Please advise.