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Material for swarf guards

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Martyn Duncumb02/11/2017 21:56:35
44 forum posts
3 photos

I want to make up some transparent guards for my mini lathe but do not know enough about plastics to choose the best material. Any help on plastic type and thickness to use would be appreciated.

Many thanks.


KWIL02/11/2017 21:58:07
3447 forum posts
66 photos

Polycarbonate sheet 5mm+

Mike Poole02/11/2017 22:12:47
3099 forum posts
72 photos

Transparent will become translucent in time, polycarbonate is very tough and will resist shattering but it is not scratch resistant, anti scratch coatings exist for applications like helmet visors but they still suffer from marks. Acrylic wil shatter and is not scratch resistant so not recommended but it is much cheaper than polycarbonate.


Muzzer02/11/2017 22:30:32
2904 forum posts
448 photos

Acrylic is also prone to cracking where solvents are present (eg coolant), IIRC. You can get polycarbonate online - or through B&Q but it's not cheap there.


oldvelo03/11/2017 09:22:04
278 forum posts
54 photos

PolyCarbonate is the way to go it can be shaped in a sheet metal folder Protect with thin cardboard sheet no heating required.

I have several for lathe and milling machine been in intermittent use for a number of years now.

Neil Wyatt03/11/2017 09:31:25
18809 forum posts
733 photos
80 articles

I use polycarbonate and it's cheap if you but a big sheet and use small bits.

I also use acrylic bearing in mind that it won't last forever in a workshop environment, but it is used for aircraft canopies. Bend by putting over a suitable template (just the corner of a piece of wood) and apply gentle heat (e.g. heat gun) and let gravity do the work.

Avoid transparent polystyrene it cracks too easily.


martin perman03/11/2017 10:15:23
2019 forum posts
86 photos

Polycarbonate can be kept scratch free by occasionally removing the scratches with the likes of Brasso, obviously dependent on depth.

Martin P

David Standing 103/11/2017 10:47:50
1296 forum posts
50 photos

Here is a sensibly priced source of polycarbonate sheet:


To polish out scratches in acrylic or polycarbonate, use Displex or Novus.

HOWARDT03/11/2017 10:50:49
801 forum posts
28 photos

No material is fool proof in guarding, you have to relate it to material size and velocity, then test it. I once saw a pit used to test turbines, the walls must have been a couple of feet thick going from steel to wood to a concrete liner. even with all the laminations blades were still embedded in the concrete. CNC machines tend to have multiple layered small windows, toughened glass, polycarbonate and steel mesh. I have seen a lathe guard where the part passed through and killed the operator. But as all say here polycarbonate of suitable thickness will prevent at least hot chips from hitting you, just don't get too close if turning something large at high speed and make it as big as possible.

peak403/11/2017 11:06:45
1545 forum posts
165 photos

If you're anywhere near Sheffield, Direct Plastics sell both plain and coated


Muzzer03/11/2017 11:19:01
2904 forum posts
448 photos

Here's what happens when you expose acrylic (PMMA) to alcohol. I expect it's to do with residual stresses combined with the ability of alcohol to diffuse into acrylic. I expect it's liable to react to other hydrocarbons in a similar way. AFAIK, polycarbonate is much more stable / inert.

Hopper03/11/2017 11:20:01
5505 forum posts
137 photos

I use old motorbike helmet visors which are mostly Lexan, I believe. Thin. Flexible, very scratch-resistant and apparently bullet proof.

You can buy sheets of Lexan but no idea of cost as I have only ever used new stuff at work. (We put it over the windows in the mental health unit at teh hospital where I worked so it was impossible to break the windows and get out etc.)

Edited By Hopper on 03/11/2017 11:42:48

Edited By Hopper on 03/11/2017 11:43:34

Muzzer03/11/2017 11:28:14
2904 forum posts
448 photos

Funny timing - I'm trying to figure out the best approach to guarding my CNC machine myself, even as we speak. The table is long enough to lay someone out on, so full enclosure won't be possible by the time you allow for 700mm of movement. I'm thinking of some form of trick curtain at the ends to contain the coolant and chips. But a sliding / hinged polycarbonate front window / door seems sensible.

With a smaller machine like a Tormach, it's possible to fully enclose the entire machine. Threadexpress ("Cluff" Hall down under) has covered this extensively and thoughtfully on Youtube. Some interesting ideas there.


Steve Pavey03/11/2017 13:19:41
354 forum posts
40 photos

I’ve just made a chip guard for my shaper from 6mm polycarbonate. I realise that it won’t stay transparent for ever, but then again I don’t actually need to look through it!

The video that Murray has posted above is interesting - I don’t know what sort of acrylic that is though, cast or extruded? The extruded type will show that sort of cracking and crazing without the flame treatment, just the heat from normal cutting, filing and abrasive polishing will be enough. The cast varieties are much more forgiving.

Neil Wyatt03/11/2017 13:45:15
18809 forum posts
733 photos
80 articles

I made the mistake of cleaning masking tape marks off a £300 display case with meths

It was fine on the ordinary surfaces, but in the two spots where it got on cut edges - crazing.


Joseph Noci 103/11/2017 14:54:02
1013 forum posts
1253 photos

Hi Martyn,

I made a guard that can flip up out the way, and can also slide away to the right, on an angle aluminium section on the top of the swarf surround guard - used Perspex, which if not known in the UK is probably acrylic - seems to work well and is easily replaced and inexpensive.


You can just see the slide on the upper part of the covers here:


Here it is flipped up - photo taken while the Lathe was undergoing refurbishment;

906-shield flipped up.jpg

910- shield down right.jpg


richardandtracy03/11/2017 15:28:35
943 forum posts
10 photos

Generally acrylic is more stable art organic fluids than PC, but, as shown, there are weaknesses. PC crazes and can shatter when contaminated with petrol, which is why I was surprised in its use for m/c helmets. I have an old PC one that I inspect closely on a regular basis, and will dump it as soon as the visor crazes.

However, in normal use for guards, PC is tougher.



Journeyman03/11/2017 16:52:38
1076 forum posts
210 photos

Definitely polycarbonate, it can be easily cut using a jigsaw and I found that you could use a plane set to a fine cut to smooth the edges. It can be drilled easily to take bolts but it will crack. I used 6mm to make guards for the lathe and mill


Gaurd on the lathe headstock to stop swarf finding it's way on to the top and under the gear box. Held in place by two magnets. It fits between the headstock and the chuck guard.


Folding guard on the mill; as can be seen polycarbonate is very clear when new. It does scratch easily and gradually becomes opaque as you clean it.


Martyn Duncumb03/11/2017 18:14:07
44 forum posts
3 photos

Many thanks everyone. What a comprehensive series of replies. You have covered everything and I particularly appreciate the warnings and hints on the negative aspects of the materials which I was not aware of.

Thank you all for your help. I can now get on with my guards.


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