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I need to lap the gibs on couple of my machines I recently purchased, (with little time to use/clean, etc., 'till now). I've never lapped gibs - any particular tips?

Dennis (really new at some of this)

Cummins Mini Mill, freshly unpacked
HF 7x10
Cummins 7x12

Dennis,

welcome to the group. If you have not already done so take a bit of time and browse through www.mini-lathe.com (without doubt the best internet resource for the mini's there is) and littlemachineshop.com which will provide you with all the basics you need toi know.

Have fun

gerry
leeds UK

From: Dennis Thompson <dbt@...>
Reply-To: 7x12minilathe@...
To: 7x12minilathe@...
Subject: [7x12minilathe] Lapping gibs...tips?
Date: Mon, 19 Mar 2007 23:20:43 -0700

I need to lap the gibs on couple of my machines I recently
purchased, (with little time to use/clean, etc., 'till now). I've
never lapped gibs - any particular tips?

Dennis (really new at some of this)

Cummins Mini Mill, freshly unpacked
HF 7x10
Cummins 7x12

_________________________________________________________________
Solve the Conspiracy and win fantastic prizes.

There isn't much to add to the instructions at mini-lathe.com. Begin
by determining if the the gibs are straight enough to be lapped and
first unbend them as necessary. It is pretty easy to get an idea if
your gibs or surface plates are flat. Just place a decent all-steel
ruler's edge up against the surface and hold it up to the light.
0.0005" error will be very obvious.

I cannot find the original source, but someone here suggested using a
drill press as an arbor press to straighten the gibs. Support the
ends with pieces of sheet metal and press down on the centre. By
using progressively thicker pieces of sheet metal, you don't risk
over-bending or breaking the gib. I found this works well.

It's hard to lap the surface of the gibs so that they don't become
convex along their width since they're thin and hard to hold (not to
mention sharp!). I found it was very much worthwhile to make a holder
for them. I just ran a short scrap block of oak through a table saw,
with the blade set to cut about 3/32" or so depth, with an angle to
match the gib's sides, and then widened it until the gib could be
tapped into the slot. Naturally the same could easily be done with a
sharp chisel, etc. Could even superglue it to a block and release it
later with acetone.

I hope this helps. If your gibs are not straight, this will
definitely make a big difference on the machine.

Hi Dennis,

I recently did the compound & cross slides on my 7x12. I think the 7x10
will be the same for you. Before you start I suggest you do the usual
gib adjustment and see how good you can get it. That will give you a
feel for how vague the adjustments are and how loose they need to be in
order not to bind at some point of the travel. When you do this again
later your eyes will pop!

I trued the gib strip on wet & dry per
www.mini-lathe.com/Lapping/Lapping.htm
<> and then lapped the
dovetail per www.mini-lathe.com/Lapping/mt_lap.htm
<> .

The carriage also needs setting up. The Sieg jack screws are a flawed
concept and I'll shim it when I get some. For now I adjusted the
Sieg thingies per www.mini-lathe.com/Mini_lathe/Tuning/tuning.htm
<> . As with the
dovetails on the slides, adjustment is a compromise to avoid binding at
some point of the travel. I expect similar improvements when I get to
shimming it and lapping the underside of the ways where they ride.

John

When I straightened mine, I used the drill press as an arbor press
with a dial indicator to show quill travel. It took deflecting the
gib strip about 0.015" to remove the 0.005" curve it initially had.
Since I was measuring quill travel I used relatively large risers to
support the piece. Using calibrated supports would eliminate the
need to measure actual quill travel.

I lapped with the strips in place, instead of lapping them
separately. Since I was trying to improve the overall contact area
it seemed logical to lap with them in their assembled location. By
the same token, I only lapped until I had reasonable surface
contact. By minimizing the amount of lapping I avoided much risk of
making the gibs convex; the actual lapping was consistent with
loathing of the process. (Used to have to do it on relatively large
steam fittings in a previous incarnation.)

Roy

--- In 7x12minilathe@..., "Paul Moir" <paul.moir@...>
wrote:

There isn't much to add to the instructions at mini-lathe.com.

Begin

by determining if the the gibs are straight enough to be lapped and
first unbend them as necessary. It is pretty easy to get an idea if
your gibs or surface plates are flat. Just place a decent all-steel
ruler's edge up against the surface and hold it up to the light.
0.0005" error will be very obvious.

I cannot find the original source, but someone here suggested using

a

drill press as an arbor press to straighten the gibs. Support the
ends with pieces of sheet metal and press down on the centre. By
using progressively thicker pieces of sheet metal, you don't risk
over-bending or breaking the gib. I found this works well.

It's hard to lap the surface of the gibs so that they don't become
convex along their width since they're thin and hard to hold (not to
mention sharp!). I found it was very much worthwhile to make a

holder

for them. I just ran a short scrap block of oak through a table

saw,

with the blade set to cut about 3/32" or so depth, with an angle to
match the gib's sides, and then widened it until the gib could be
tapped into the slot. Naturally the same could easily be done with

a

sharp chisel, etc. Could even superglue it to a block and release

it

later with acetone.

I hope this helps. If your gibs are not straight, this will
definitely make a big difference on the machine.


--- In 7x12minilathe@..., Dennis Thompson <dbt@> wrote:

I need to lap the gibs on couple of my machines I recently
purchased, (with little time to use/clean, etc., 'till now).

I've

never lapped gibs - any particular tips?

Dennis (really new at some of this)

Cummins Mini Mill, freshly unpacked
HF 7x10
Cummins 7x12

I wrote a long instructional on this some years ago, which is posted on
the mini-lathe site at If
I were doing it again, I'd use a coarser abrasive, such as fine
valve-grinding compound.

Mike Taglieri miket--nyc@...

Everyone has his reasons.
- Jean Renoir "The Rules of the Game"


On Mon, 19 Mar 2007 23:20:43 -0700 Dennis Thompson <dbt@...>
writes: