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Old 18th August 2006, 12:08 AM   #21
bulgin is offline bulgin  South Africa
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Join Date: May 2006
Default Milling dead centre perpendicular

Hey Guys!

I am humbled and overwhelmed by your kind offers of links, solutions and goodwill in assistance to solve a problem. Some time ago, someone here wrote me how to post a pic or line drawing and I will try to do so soon as I have both line drawings and pictures.

My only further problem is that the component is something I developed over a 6 year period and which forms part of very expensive design registrations in the EEC and in the US now in process.

In the meantime, I'll do my best to describe the widget a bit further. It is first turned down from an engineering plastic of which the gross dia is 15mm roundbar, the thinnest stock I can buy. I cut off a piece of say, 35 or 40mm long, chuck it in the lathe and turn about 18mm of the front end down to first 7mm. Next, I turn a portion of the forward end of 7mm down to 6mm and give it a rounded profile with a special cutter.

I then remove the stock from the lathe chuck and turn it around and reduce the original 15mm by +- 10mm long to a thickness of 5mm x 15mm. I then put a 7mm 4-flute cutter in the tailstock chuck and mill a 1mm recess and give it a whiff of engineers' blue. Next, I 'kiss' that end with a sharp cutter so that only a 1mm blue coloured recess is visible.

This blue 'dot' describes the space for the 4 cartridge pin config.

When this is done, I take the job to the milling machine and mill off the remaining 15mm round section so that it becomes square (+-8'5x8.5mm), with only a little 'meat' remaining around the blue guide dot and which is the actual width of the Mantis cart.

At this time, the contraption is ready for drilling 4 cart. pin holes within the blue dot, plus first a 1.5mm angled hole deadcentre between the pin holes and the same hole recessed 4mm deep x 2mm dia.

All plain sailing up to now (and 1 hour later)! and in your sweaty mitt you now have a piece of plastic 25mm long, the rear end 8.5x8.5 square and the forward end in two diameters of 7mm and ending in a step to 6mm dia., turned to have a ball profile at the front end.

If you are still with me (Yawn!), this is basically the size into which I have to mill an angled 5mm recess and drill 3 more holes for threading and milling 3 further 1.5mm slots and lastly, 2 1mm slots along the side.

The person I commissioned to CAD draw this device and the other bits is a properly qualified Pr design engineer - one of the very best in ZAR. He drew this thing for me and he has serious doubts if this device could be injection-moulded due to its complexity. So, here I am, bound to my milling machine and looking for a way out to reduce a 40% waste factor.

One of the diy'ers mentioned boring tools. No problem - I have them but these can't be used due to the size of the job and the angles involved. Instead I use the best quality, sharpest milling cutters money can buy.

Thank you once more to all of you kind people. I'll check out the laser links and report back

Regards to all

bulgin
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Old 18th August 2006, 12:30 AM   #22
diyAudio Member
 
Join Date: Jan 2003
Location: Musicville
Default Re: Milling dead centre perpendicular

Quote:
Originally posted by bulgin
One of the diy'ers mentioned boring tools. No problem - I have them but these can't be used due to the size of the job and the angles involved. Instead I use the best quality, sharpest milling cutters money can buy.

Thank you once more to all of you kind people. I'll check out the laser links and report back

Regards to all

bulgin
Hi Bulgin, I mentioned boring tools. I have been a machinist for 30 years now and own and operate my own fully equipped machine shop. Boring tools can be purchased to bore a hole as small as 0.020" (.5mm) You are putting too much tool pressure on the delicate part by using an end mill, sharp or not. The end mill also has relief so you are not getting a counterbore that is flat at the bottom, not sure if you care but nevertheless, too much tool pressure.
I'd like to see exactly what the part looks like. It doesn't seem like it would necessitate a 40% rejection rate.
Using an end mill would be a LAST resort, and keep in mind the wall thickness is going to vary.
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Old 18th August 2006, 12:46 AM   #23
diyAudio Member
 
Join Date: Jan 2003
Location: Musicville
I should clarify that the boring head I mentioned is used on a milling machine, not a lathe.
http://www.criterionmachineworks.com/

You can bore accurate holes as small as 1.5mm with these miniature boring bars. They can be purchased here.
http://www.sct-usa.com/bb1.asp

There are other sources I can provide if this is something you are interested in.
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Old 18th August 2006, 11:38 AM   #24
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I am still learning!
Didn't know boring bars came that small.
I had always thought those tiny holes were drilled.
__________________
regards Andrew T.
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Old 19th August 2006, 01:06 AM   #25
bulgin is offline bulgin  South Africa
diyAudio Member
 
Join Date: May 2006
Default Milling dead centre perpendicular

Hi vinyladdict

I know about the 'bump' in the centre of a hole milled by a 4-flute cutter. This however is no problem as a 2mm hole is drilled on the raised are. I get your point re miniature boring bars and the surmising about too much pressure on the cutter. Its plastic being machined and very delicate hands are needed to avoid deflection during cutting.

Thanks for all the tips, links and willingness by all who posted here.

Maybe there could be some public domain news about what I've made in a week or two!

bulgin
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Old 19th August 2006, 01:56 AM   #26
diyAudio Member
 
Join Date: Jan 2003
Location: Musicville
Default Re: Milling dead centre perpendicular

Quote:
Originally posted by bulgin
Hi vinyladdict

I know about the 'bump' in the centre of a hole milled by a 4-flute cutter. This however is no problem as a 2mm hole is drilled on the raised are. I get your point re miniature boring bars and the surmising about too much pressure on the cutter. Its plastic being machined and very delicate hands are needed to avoid deflection during cutting.

Thanks for all the tips, links and willingness by all who posted here.

Maybe there could be some public domain news about what I've made in a week or two!

bulgin
Hi Bulgin, Center cutting end mills won't leave a "bump". I was talking about the relief angle on the bottom cutting edge of the end mill. FWIW, a 2 flute e/m (again less tool pressure) would be best for counterboring but since you drilled a pilot hole there would be no bump anyway.

What type of milling machine do you have?
Can you use collets in the spindle or are you only able to use a Jacobs chuck.
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