Help for beginner please

This topic has 14 replies, 8 voices, and was last updated 8 November 2016 at 01:11 by John Stevenson 1.

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7 November 2016 at 14:04 #265260
john dakin
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@johndakin59277
i need to cut a circle out of 3mm brass sheet, the disc is 100mm diameter with a 10mm mounting hole in the centre, I could do with help on how to do this on a cnc Bench top machine, I needs feeds and speeds, do I use conventional or climb milling, what type of cutter to use, and what direction of cut for internal and external cuts, any advice or help on this please, I'm trying to get a decent finish
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7 November 2016 at 14:04 #8370
john dakin
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@johndakin59277
7 November 2016 at 14:23 #265262
Martin Connelly
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@martinconnelly55370
Mach3 Mill has a wizard for feeds and speeds. It needs basic information such as cutter diameter, number of flutes and the machine's maximum spindle rpm. Tell t what material you have and the size of chip to go for. I would suggest 0.125mm or 0.005" for chip size.

What diameter cutter are you proposing to use?

Will the centre of the disk be x=0, y-0?

Will the top face be z=0?

Martin
7 November 2016 at 17:11 #265291
john dakin
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@johndakin59277
I am thinking of using a 3mm cutter and the z and y are 0 and top face is 0
7 November 2016 at 17:28 #265296
Martin Connelly
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@martinconnelly55370
Hole in the centre with 3mm cutter. Since you are cutting a slot climb or conventional has no relevancy. You will need to set the feed rate based on the number of flutes.

g0 x8. 5 y0 z5

g0 z0

g03 x3. 5 y0 z-1 i-3.5

g03 x3. 5 y0 z-2 i-3.5

g03 x3. 5 y0 z-3.25 i-3.5

g03 x3. 5 y0 i-3.5

g03 x0 y0 z5 i-1.75

Outside edge

g0 x51. 5

g0 z0

g02 x51. 5 y0 z-1 i-51.5

g02 x51. 5 y0 z-2 i-51.5

g02 x51. 5 y0 z-3.25 i-51.5

g02 x51. 5 y0 i-51.5

g01 y-5 z5

This is unchecked and off the top of my head so check the tool path display before use. Also have waste material below the material. I would suggest using double sided tape under the stock to keep it steady as the cut separates it from the waste.

Martin
7 November 2016 at 17:40 #265297
JasonB
Moderator
@jasonb
Not being a CNC chap and only guessing that the G code is taking about 3 passes on finished size would a better finish that John desires be obtained by say cutting in 3 passes at 51.7mm and then a full depth climb cut taking the last 0.2mm off, Thats how I would do it if using the rotary table on a conventional mall.

John, can I ask if you have any experiance with conventional manual mills or have you jumped in straight at the deep end with a CNC machine, this may help others with their answers.

Edited By JasonB on 07/11/2016 17:45:35
7 November 2016 at 18:13 #265305
Emgee
Participant
@emgee
No doubt a final pass of 0.20 or even 0.10mm would achieve a good finish, it all depends on the machine type and setting speeds/feeds to the optimum. Personally I would use a full depth finish climb pass on my Emco F1 cnc mill.

Emgee

Edited By Emgee on 07/11/2016 18:15:09
7 November 2016 at 19:40 #265318
john dakin
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@johndakin59277
Thanks for all the advice guys, I am a total novice, and yes I have jumped in at the deep end, but have a good understanding of the basic procedures.
7 November 2016 at 19:57 #265323
Bazyle
Participant
@bazyle
Have you thought about how the sheet will be held down and what it will be mounted on as that will get cut too.
7 November 2016 at 20:36 #265332
john dakin
Participant
@johndakin59277
Yes, I have made a holding jig for the part
7 November 2016 at 21:13 #265337
Ian P
Participant
@ianp
Posted by john dakin on 07/11/2016 20:36:47:

Yes, I have made a holding jig for the part

I'm intrigued!

The part you are making sounds like a large washer, if you are machining the OD and the ID what does the jig grip?

Ian P
7 November 2016 at 22:32 #265344
John Stevenson 1
Participant
@johnstevenson1
OK 100mm washer, zero at 0,0, cutter is 3mm 2 flute, 3 flute or centrecutting 4 flute.

With 4 tabs to hold the washer in, clamps on the unwanted corners.

Code here.
7 November 2016 at 22:48 #265346
john dakin
Participant
@johndakin59277
Ha, thanks so much that's exactly what I needed, I had a jig that held a 100 x 100mm square plate and the part was then cut out, the centre hole first, then another jig was placed on the machine bed with a raised stub that the centre hole would locate onto, the stub was threaded and the part was bolted to that, your idea is much quicker and easier, thanks so much for your time and advice on this it's been a great help
7 November 2016 at 23:17 #265348
Bob Stevenson
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@bobstevenson13909
Interesting, intriguing and amazing!

How many of these are you making?

I cut out clock wheel blanks by drilling centre then mounting in lathe and 'knifing' out the blank to size using a knife tool of my own making. It takes about 4 minutes to make one although sometimes I cut two, or very rarely, three at the same time. How long does it take to CNC these?….how long to design or program?
8 November 2016 at 01:11 #265351
John Stevenson 1
Participant
@johnstevenson1
Posted by Bob Stevenson on 07/11/2016 23:17:58:

Interesting, intriguing and amazing!

How many of these are you making?

I cut out clock wheel blanks by drilling centre then mounting in lathe and 'knifing' out the blank to size using a knife tool of my own making. It takes about 4 minutes to make one although sometimes I cut two, or very rarely, three at the same time. How long does it take to CNC these?….how long to design or program?

.

About 5 minutes the program, took longer to write the reply than do it.

Depends on the OP how long to cut depending on his setup. I did the code because he asked about doing it with CNC. He didn't ask about trepanning.
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