Note,should you have a saw blade with no riving knife,the use of a suitable wooden wedge in the saw cut in the wood behind the blade also works well,a second pair of hands can be usefull here.
A good picture of a circular saw blade with a riving knife behind it.
The riving knife pictured below should not be used,it has an open lower end and should the bolts come loose,the blade itself could come out and hit you,so weld this type closed at the bottom.
I am pleased I never took on as an apprentice wood machinist,most I knew have one or other finger missing,some lost a hand,I can still remember one incident with an up right spindle,the guy got his hand too close,nasty result. As apprentices,we were not allowed to use a circular saw with out a Riving Knife,thats a curved steel plate behind the blade,which was supposed to match the width of the set of the blades teeth.At that time tungsten teeth were not invented and what would happen was as the set of the teeth wore out,the blade would (could) grab the wood and chuck it back at you,the riving knife stopped that as the wood could not close on the blade,we never see riving knives now of course,except in saw mills.Picture to follow a little later.
Check this link now to read sheet 16 on woodworking practice:
http://www.hse.gov.uk/pubns/wis16.pdf
D&T subject leaders in
Schools with secondary age children Bill Dewar
Kingston Centre
Fairway, Stafford. ST16 3TW
Telephone: (01785) 277900/1
Fax: (01785) 256193
Please ask for: Tim Brotherhood
Email: tim.brotherhood@staffordshire.gov.uk
Direct: 07800 626 534
Cc: Steve Brown, Mick Devall September 2005
Ref. : S:\DEV-GRPS\CURRIC\D-and-T\A-Secondary\Health & Safety\Letters\Alert Sep 2005.doc
Circular Saws – Riving knife
Dear colleague,
County Technicians have alerted me to two issues with circular saw riving knives.
Riving knife thickness
To be effective the thickness of the riving knife must be greater than the saw blade body but less than the width of cut. A small number of schools have recently purchased tipped blades imported from the Far East and the blade body is thicker than normal making the riving knife ineffective.
Illustration taken from
HSE Woodworking
information sheet 16
www.hse.gov.uk
If this applies to your machine you must stop using it until this issue has been resolved.
Either:
1. Replace the blade with one whose thickness is correctly matched to the riving knife;
Or:
2. Replace the riving knife with one whose thickness is correctly matched to the new blade.
Open mounting slots
One or two riving knives have been found to have open mouning slots possibly to allow easier maintenence. Should the knife become loose it could be ejected from the machine and caouse injury.
The bottom of the
mounting slot
must be closed
For this reason riving knives must have closed mounting slots.
If your riving knife has open mounting slots you must stop using the circular saw until a riving knife with closed mounting slots has been fitted.
Action
If you have a circular saw in your department you should arrange for it to be checked as soon as possible for these problems. Any shortcomings must be put right before the machine is used again.
Remedial work can be carried out in school by someone qualified to use the machine or through the County Technicians Service. (Mick Devall Tel:01889 256290)
If you would like further information or need to discuss this matter further do not hesitate to contact me.
Many thanks
Tim Brotherhood
Adviser for design & technology
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