Many milling machines with a quill style head use a quill lock based on the original Bridgeport design as shown in the photo..
This instructable describes a very simple modification which prevents the drag on the quill which is quite common on these milling machines,
Other than having your milling machine no other materials are required. The only tool that might be necessary is a pair of pliers.
Step 1: The Problem
The photo in the introduction shows the lock in the locked position. The small lever is in the down position, and there is no problem.
The photo in this step shows the lock freed off with the lever in the upper position. This often creates a problem because gravity, aided by some vibration when the machine is running, can pull the lever down creating drag on the quill. In general this will not lock the quill completely but it will add some drag which is particularly noticeable when peck drilling and similar operations.
Step 2: Dismantling
Firstly remove the small operating lever. This is just screwed in with a right hand thread. I could unscrew mine by hand but if yours is tight then you can use a pair of pliers.
With the lever removed it should be easy to unscrew the clamp bolt by hand, this is also a right hand thread. The first photo shows the head of the bolt with the lever removed. With the bolt removed the two bronze clamping blocks can be pushed out. The front block has a through hole but the rear one is threaded for the bolt.
The other photos show the component parts.
Step 3: Reassembly
All we need to do is to fit everything in reverse. That is, fit the threaded block to the front and the one with the through hole to the rear. Make sure that the cut outs are aligned with the quill body. Replace the bolt but insert it from the rear. Screw the lever back in place on the bolt.
Now what we have done is to reverse the action of the lock. The quill is locked with the lever in the higher position but as it is tight in this position it does not drop down. On the other hand the lever hangs down when loosened off and hence there is no tendency to tighten.
That is all there is to it. Two minutes work and zero cost fixes what was a very annoying problem.
Step 4: The Movie
Here is a short three minute video showing the whole process.
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