Flat bottom holes

Flat bottom holes

This topic has 6 replies, 6 voices, and was last updated 24 October 2011 at 16:14 by colin hawes.

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23 October 2011 at 16:15 #76711
Tony Martyr
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@tonymartyr14488
I have never been able to get a decent flat bottom to a hole in a bronze valve casting using a home-made D-bit, chatter or an undulation has resulted. The next job I have to do is not a blind hole (more difficult) but a 9/322 flat bottom hole with a 5/32 through drilling into which the 45 deg valve spindle head screws. Having given up on D bits I think I will buy a 9/32 slot milling cutter to do the job in an expensive bronze casting.

Is this sensible?

Tony
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23 October 2011 at 16:15 #5716
Tony Martyr
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@tonymartyr14488
23 October 2011 at 16:44 #76715
David Littlewood
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@davidlittlewood51847
Tony,

I have used slot drills before to make flat bottomed holes; it works quite well provided the component itself is pretty solid and cannot bend. If the component has a through hole, you could use a spot-face cutter instead. For flimsy components such as O gauge coupling rods (in which I needed to make a recess for a retaining bush) they have the advantage that the component will not shift and cause a spoiled job. With a substantial item, the slot drill should be fine.

David
23 October 2011 at 21:04 #76732
JohnF
Participant
@johnf59703
Hi Tony,

Its worth buying a 3 flute slot drill they are stiffer and more stable when cutting so less likely to chatter.

An FC3 cutter would probably fill the bill–try J & L Tools they someitmes have them on offer http://www.mscjlindustrial.co.uk/cgi/insrhm

John
23 October 2011 at 21:19 #76735
Terry Lane
Participant
@terrylane
I’ve always had much better results with an ordinary ‘D’ bit rather than end mills/slot drills tho’
23 October 2011 at 22:31 #76741
Anonymous
Conversely, I’ve never had a problem using slot drills in the lathe and vertical mill to make flat bottomed holes.

The only caveat I would add is that in bronze a positive rake slot drill may have a tendency to get dragged into the work, in similar fashion to a twist drill. This can be ameliorated by ensuring that the setup is rigid and, more importantly, keep the feedrate up. Use a fairly aggressive feedrate, stop at depth and immediately back out.

Regards,

Andrew
24 October 2011 at 16:14 #76779
colin hawes
Participant
@colinhawes85982
Tony please note that slot drills are not ftat on the end but relieved to their centre to aid their guidance.To get a flat bottomed hole means regrinding a slot drill’s end.
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