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Joe gwinn Joe gwinn is offline
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Default Incorrectly tapped hole

On Tue, 15 Sep 2020 14:04:10 -0700, Bob La Londe
wrote:

On 9/14/2020 6:26 PM, wrote:
I recently bought a lathe. Part of the promotion was an LED light. I
just received the light. Wanting to mount it on the headstock, I
found the holes in the headstock are incorrectly tapped. The mounting
location on the tailstock are correct. I really don't want it on the
tailstock.

The incorrect holes are drilled/tapped M3.5x.35mm. They should be
M4x.70. M3.5X.35 is a "standard" M3.5 fine thread but these things
are unicorns. I haven't found them anywhere, including Amazon,
Grainger, Bolt Depot, and Fastenal.

I've sent the manufacturer an email but have heard nothing. I sent
one with pictures of the problem but it bounced (images are rather
large, so understandable). I resent it without the pictures. Anyway.

1) How to correct?
a) The difference in diameter is less than the thread depth so
retapping to M4x.70 doesn't seem to be an option.
b) An M5 screw doesn't fit through the lamp holes.
c) M3.5x.35 is a "standard" M3.5 Fine thread but they're unicorns.
I've checked Amazon, Grainger, Bolt Depot, and Fastenal. No
joy.
d) The bracket is cast iron and also holds the spindle copying
fixture and is quite complicated. Copying it wouldn't be
a simple matter.

2) How the hell does this happen? Aren't these things made with CNC
tools? Both the drill and tap were loaded wrong? As far as I know
there aren't isn't any other M3.5 hardware on the lathe.

I'm not really optimistic that the manufacturer is going to answer
anytime soon. Two months after I bought the lathe I called to find
out where the promotional lamp kit was. I got no answer. The customer
support number on the paperwork had been disconnected. Another number
on the web site had a message that the phonemail inbox was full. I
don't remember how I finally got a message through but a week or two
later I got a call from Woodcraft corporate office (I bought the lathe
at a local store). Maybe I'll get another call from Woodcraft in a
couple of weeks. This wasn't a cheap tool. Not happy but amazed at
how this could happen.


A quick check shows a 3.5 hole will give you 53% thread form for an M4
thread. 75 would be better in cast iiron or aluminum, but 53% will hold
just fine if you don't act like a ****** with a spanner. Knock yourself
out and drill and retap it. Problem solved.


Or, drill and tap for a M4 helicoil.

Joe Gwinn