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Suggestions for flat-bottom bore 12.2" deep x 1.9" dia in polypro?

specfab

Titanium
Joined
May 28, 2005
Location
AZ
So my best customer dumps this prototype job on me a few weeks ago, consisting of 3 assemblies of one type and 2 of another. The (2)pc job involves a housing made from polypro rod, nominal 2.5 OD, by 15.85" long, along with about a dozen other parts. There is a flat-bottom bore finishing to 12.16" deep (on center), 1.91" diameter. I have made similar parts before, nothing this large, though. The bore bottom does have a .32 dia center hole leading to another smaller bore from the opposite end of the part. Tolerances can be +/- .010, finish on the bore bottom needs to be good enough for an o-ring seal.

I am envisioning steady rest and drilling from the toolpost, then boring, although I have yet to look in detail at the real estate layout on my Clausing 12x36 to see that this is actually possible.;-) I'm also considering that this may be the time when I finally have to buy a right-angle head for the BPort. Finding a suitable boring bar is also a challenge, as may also be avoiding ripping the toolpost off the compound with 13" of boring bar lever to work with...

Any smart suggestions will be eagerly considered.
 
Iposted my recipe for this sort of job on the CNC forum a month 6 weeks ?at the most back,......look up ''deep hole in nylon'' or something.
 
Thanks, guys --

jhruska, I was already halfway down that road you suggested; completed a purchase on eBay for same.

Limy Sami -- I read through your dissertation;-) I hope I can simplify somewhat, but your guidance is pretty clear. Thanks -
 
Buy a spade drill? I think you could make one fairly easily. Get some fairly hard tool steel and soft solder it onto a 1" rod or piece of 1" round tubing then add in cutting geometry. The steel doesn't even have to be heat treated for such a soft plastic. You will need to predrill to diameter before using a flat
ottom spade, though.

Make sure the bar is strong enough torsionally or it'll chatter.

Sent from my XT1053 using Tapatalk
 
Thanks, guys --

jhruska, I was already halfway down that road you suggested; completed a purchase on eBay for same.

Limy Sami -- I read through your dissertation;-) I hope I can simplify somewhat, but your guidance is pretty clear. Thanks -

The spade will have chipbreakers? Yes?
Otherwise chip control might get a little weird.
John
 
snipped

...avoiding ripping the toolpost off the compound with 13" of boring bar lever to work with...

I would mount the boring bar straight to the cross slide minus the compound and toolpost.

Polypropylene chip control is a problem in deep bores. What works for me is to start the cut, then stop the lathe with the feed still engaged. Grab the poly's chip and de-tangle it, stick it in a strategically placed vacuum cleaner's hose then start the lathe back up. You may have to reduce the hose's opening to get enough suction.
 








 
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