A Belt Guard for the Taig Lathe

Making things a bit safer

Part of the Making Stuff collection
by Douglas W. Jones
THE UNIVERSITY OF IOWA Department of Computer Science

The Problem

Most small lathes are run without belt guards. I've found only a few exceptions:

There are two good reasons to want a belt guard:

Guards on lathe chucks are a bit problematic — all of the machinists I've spoken to hate them and defeat them whenever possible. OSHA rules require them and workplace inspections demand that they be present, but in use, they end up being pushed aside.

Perhaps someday, I'll make a chuck guard that I can push aside, but this web page is about making a belt guard. Another thing on my "someday" list is a chip shield for the toolpost. This is something I particularly want when I'm turning hardened steel, because those chips are hot enough to threaten burns when they land on you.
The belt guard before folding
a flat pattern cut from sheet steel

To start with, I finished my motor mount and measured the geometry of the belt relative to everything. I tried out various belt guard designs using folded paper and cardboard, and when I finally satisfied myself that I had a good design, I transferred the design to 22 gauge (0.0299" or 0.76mm) mild steel and cut it out. The above photo shows the result, before I began folding it.

Note: I've occasionally thought of making or getting a brake for sheet metal bending, but I don't have one. What I do have is a bench vise and random pieces of steel and wood. To bend sheet metal such as I used for the belt guard, start by clamping the metal in the vise. For short bends such as the tabs used to secure the ends, clamp the tab directly in the vise. I did all the short bends first. For long bends, I used structural steel angle to extend the vise jaws as needed, with auxiliary C-clamps at the ends to make sure the metal stayed tightly clamped.

The actual bending operation is done with a hammer and a block of hardwood. I used a 4" cut-off from a 3/4"×2" piece of hard maple, holding the end grain against the metal and tapping with a drilling hammer. The goal with each hammering pass is to bend the sheet only a few degrees. In mid pass, half the fold will be bent at a sharper angle than the other half, and what ought to be a flat sheet will be significantly warped. The idea is to keep the change in angle small, so that that the only place you exceed the yield strength of the metal is along the bend itself, while all the rest of the metal is within its elastic limit and will spring back to being flat once the bend is completed.

Mounting hardware
details of the belt guard mounting hardware
None of the weight of the belt guard is carried by the motor, as that would change the belt tension. At the motor end, a clip holds the belt guard snugly against the face of the motor so it won't rattle, but the clip does not support any weight.

The entire weight of the belt guard rests on an adjustable foot that sits on top of the lathe base. The leg is made of steel bar, forged to a 90° bend at the base to make a foot. The foot is drilled and tapped 10-32 for the adjustment screw. That screw began as a stainless steel Phillips pan-head screw. The screw goes up through the foot and a locking nut.

The screw sits on the cover of the lathe base directly over a microswitch that prevents lathe operation except when the belt guard is installed. The connection from the foot to the microswitch is through a small hole in the cover and a pin that slides in a hole drilled axially through the foot. This pin also holds the foot in alignment so it doesn't slide sideways. The top end of the pin is threaded 0-80 and screwed into an adjusting cap that screws onto the top of the adjusting screw, and there's a second lock nut for the cap.

The second mounting bracket is cut from a piece of angle iron. This mounts to the top of the headstock with a T-slot bolt and a single wingnut. Note, the wingnut is pushing down on the belt guard, counterbalancing the weight of the guard that would otherwise rest on the motor, so all of the weight is on the foot. The line between the mounting bolt and the center of gravity of the whole assembly is very close to passing over the foot, so the side forces the belt guard applies to the headstock and motor are small.

I added a cabinet door handle to the top of the guard, centered above the center of gravity of the whole assembly, so that you can easily lift the guard, one handed.

Note that all of the screws used to hold parts to the belt guard are flat-head screws with their heads on the inside. Some of them are fairly close to the belt when it is in some positions, and it is important that none of them are able to snag on the belt or cut it.

The belt guard in use
belt guard installed seen from above
Currently, the belt guard is held together by screws and nuts in bent tabs. Someday, I'll consider braizing the joints.

The belt guard has worked well. If you're stupid enough to pull the guard from the lathe while it's spinning, you need two hands to do so, one to hold the handle on the guard and the other to loosen the wingnut. The motor power is cut the moment you start to lift the guard, and by the time you've got the guard clear of the pulleys, everything has come to a halt.

Taking off the guard to move the belt to a different speed setting is fast enough that it's not a problem.

My only complaint about the design of this belt guard is that I have to remove any drawbar from the headstock before I remove the guard. The hole in the side of the belt guard is there to pass the drawbar, but I am tempted to cut a slot from the hole to the bottom edge of the belt-guard side.

The belt guard stowed
belt guard stowed under lathe bed
When not in use, the belt guard fits comfortably on the lathe's base board under the lathe bed.