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Myford ML7 - Chuck Guard

UNDER CONSTRUCTION - requires links

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I made a Chuck Guard for the ML7.

The Guard contains the oil that flies off the spindle and chuck, and contains the oil and swarf from the work being cut.
The front area around the lathe is noticeably clearer of swarf.

Some of the oil from the drip feed oilers leaks out from the spindle bearings, just behind the chuck, and can be flung forwards into the middle of the workshop.
To contain as much oil as possible, the Guard is a close fit around the spindle area behind the chuck.

The Chuck Guard does not have a safety switch to cut the power when the guard is open. A safety switch could be fitted easily, if required.

There are a couple of disadvantages to my Chuch Guard configuration:-
The blade in my parting tool is quite long, and protrudes from the rear of the QCTP tool holder. As a consequence, the rear of the blade can collide with the acrylic of the Chuck Guard.
To overcome this I part with the guard in the up position.
A better fix would be to either reduce the length of the parting blade, or modify the acrylic. I am still pondering this.

The Chuck Guard takes up room around the chuck, and this makes it just a little more awkward when using digital calipers to measure work in the chuck.

 

 

Index :

1. Overview
2. Horizontal Support Post
3. Vertical Support Post
4. Guard Support Rod
5. PVC Guard Holder
6. Guard Height Adjuster Assembly
7. Acrylic Guard Assembly

 

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1. OVERVIEW

 

 

↓ Here is the support frame and components.

 

↓ Here the support frame attached to the back of the lathe bed.

Note the rounded ends to avoid sharp corners.
Note the cut out in the Vertical Post, to clear the headstock.

 

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2. HORIZONTAL SUPPORT BAR


The Horizontal Support Bar is secured to the lathe by two 1/4 inch BSF socket cap screws.
The two 1/4 inch BSF socket head cap screws screw into two of the existing 1/4 inch BSF tapped holes on the rear of the lathe bed.
To remove the sharp corners on the Horizontal Support Bar, I milled a radius on the end the bar. If I reach behind the lathe bed when cleaning I will not catch my hands on any sharp corners.
The two holes for the BSF socket head cap screws are counterbored using a 7/16 inch slot drill, to a depth of 8mm.
The Horizontal Support Bar is made from 19mm square EN3 bar, and is 300mm long.

 

 

 

 

 

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3. VERTICAL SUPPORT POST


The Vertical Support Post is secured to the Horizontal Support Bar with a 6mm socket head cap screw.
A section of the Vertical Support Post is cut away, to clear some features on the back of the ML7 head stock.
I milled a semi-circular profile on the top of the Vertical Support Post, to remove the sharp corners. The semi-circular profile blends in with the profiles of other features on the ML7 motorising assembly.
The Vertical Support Post is made from 19.05mm x 12.7mm (3/4 inch x 1/2 inch) EN3 bar, and is 240mm high.

 

 

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4. GUARD SUPPORT ROD


↓ Guard Support Rod

The Guard Support Rod is made from a 155mm long x 6mm diameter rod salvaged from a printer.
The PVC Guard Holder (see below) rotates around the Guard Support Rod.

↓One end of the Guard Support Rod is threaded M6.

 

 

↓The Guard Support Rod screws into the Vertical Support Post.

 

↓The opposite end of the Guard Support Rod has a 2.5mm cross drilled hole. A tommy bar, or a 1.5mm allen key, can be inserted into the hole, to help fully tighten the bar into the Vertical Support Post.

 

↓ The opposite end of the Guard Support Rod also has a shallow 8mm long groove near the 2.5mm hole. This groove is used to retain the PVC Guard Holder on the Guard Support Rod (see below).

 

↓There is an M5 threaded hole in the rear of the Vertical Support Post. An M5 socket head grub screw is screwed into this hole, and bears down onto the thread of the Guard Support Rod.
This prevents the Guard Support Rod coming loose due to vibration, or due to the rotation of the PVC Guard Holder.

 

↓M5 locking screw inserted.

 

↓ A 4mm brass pad is placed under the end of the M5 socket head grub screw, to stop the grub screw damaging the M6 thread on the Guard Support Rod.
Here is the pad and M5 screw.

 

↓ You can see two marks where the pad has pressed against the M6 screw thread.

 

I had to make a 4mm punch and die to make the 4mm pad accurately. Click here to see the punch and die.

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5. PVC GUARD HOLDER


The PVC Guard Holder is made from thick PVC sheet.
The holder is 142.5mm long x 29mm wide x 12mm thick.
The milled slot is 4mm wide and 10mm deep.

 

↓The 4mm thick Acrylic Guard Assembly fits into the slot.

 

 

↓ Two M3 screws pass through the holder. When they are tightened they compressed the holder around the Acrylic Guard, to hold it firmly.
The PVC is threaded on both sides of the slot.

 

 

↓There is an M5 tapped hole on the back of the PVC Guard Holder.
A socket head grub screw is screwed into this hole and enters the groove in the Guard Support Rod.
This retains the PVC Guard Holder on the Guard Support Rod

 

↓A PVC cylindrical spacer is located on the Guard Support Rod.
The spacer is 6mm ID, 11mm OD, and 12mm long.
The spacer keeps the PVC Guard Holder the correct distance away from the headstock.

 

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6. GUARD HEIGHT ADJUSTER ASSEMBLY


The Guard Height Adjuster assembly is used to precisely set the 'closed' position of the Acrylic Guard.
The Height Adjuster assembly is fixed to the Vertical Support Post with an M5 screw and spring washer.
The main body of the Height Adjuster is made from 12mm thick aluminium.
The component started out as a rectangular block. I milled it to fit around the Vertical Post, fitted the height adjuster screw, and then milled off the corners to make it look nice.
The adjuster screw is M5, and has a spring washer and lock nut to prevent movement from vibration.

 

 

↓ I faced the top surface of the bolt head in the lathe, to remove the raised markings and make the surface flat and smooth.

 

 

 

↓The adjuster screw bears on the PVC Guard Holder.

 

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7. ACRYLIC GUARD ASSEMBLY


The Acrylic Guard Assembly is made from 4mm thick CAST acrylic sheet.
The Acrylic Guard Assembly consists of two separate pieces, the main bent piece, and a side panel.
The bend in the acrylic piece that fits into the PVC Guard Holder was made using a home made Nichrome heater wire acrylic bender. Click here to see the bender.

The side panel of the Acrylic Guard Assembly was joined to the main bent piece using Methyl Ethyl Ketone, or MEK. The MEK is also known as Butanone. It dissolves polystyrene and many other plastics. It will 'weld' acrylic pieces together. I have also used it to weld PVC to acrylic and polycarbonate.

Update-30th August 2020
I ran the carriage into the Acrylic Guard Assembly. The force of the run in caused the side panel to become detached from the main bent piece. The solvent weld was not strong enough, and the two pieces separated at the join. There was no damage to the Acrylic. The two pieces did not 'fuse' together permanently, as I expected they would. I rejoined the two pieces again, using MEK as before.
Conclusion: MEK will bond cast acrylic to cast acrylic. MEK does not provide a really strong bond when joining cast acrylic to cast acrylic.

When the piece was bent using the Nichrome heater, the hot acrylic at the edges 'bellowed out', causing the edges to become raised. I set the bent piece of acrylic up in the mill and milled the two edges, to remove the raised sections and to make things more presentable.
The acrylic bend inwards of the edges is nice and uniform and did not require attention.

I had to make jigs for setting the acrylic up in the milling machine, and jigs for welding the side panel onto the bent piece of acrylic. I also had to make a Nichrome heater. It was a long process with a hell of a lot of experiments, trials, and error!

After all the bending, drilling, milling, and welding, there are no stress crazing/fractures on the acrylic.

 

 

 

↓The side panel of the Acrylic Guard Assembly is shaped to follow the contours of part of the spindle and the back gear lever. I finished forming the curves using a drum sander mounted in the milling machine. I got the Silverline drum sanding kit from Toolstation (it has been useful).

 

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