Throwaway Chutewidth and SmallestGrip

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Author avatarGareth Green | Last edit 18/07/2023 by Gareth Green being drafted

Technical Bulletin

...Software version has a new algorithm to control waste. see

TB Number: 372
Originator: Gareth Green
Machine: TwinCAT ZX5, ZX4, ZX3, Saw, Autoflow
Date: 11/01/18
Circulate to: Service
Title: Software Settings for dealing with small offcuts


Dealing with a short offcut at the end or start of a bar is surprisingly complicated. Dealing with one case can easily create a problem in another area. This TB seeks to explain the parameters used and give guidance on how to get the best setup. PLEASE NOTE: There will NEVER be a one-size fits all to this complex situation. All customers and all profiles are different

Definitions and Parameters

Note – these parameters have been built up over the years and may only exist in the latest software versions and later.

Parameter Definition Range Notes
minable Measurement of area at the gripper end of the bar. If an operation appears in this area, this amount is added as a waste to the bar length. This stops the cutters machining the gripper. The amount is normally determined by the length of the gripper, and / or the distance of the outfeed clamps to the cutter centreline 0-200 This is often how and why a problem offcut is created at the gripper end of the bar– if the minable is bigger than the chutewidth, there will be a regular need to cut into throwawayChunks
maxable Measurement of area at the non-gripper end of the bar. If an operation appears in this area, this amount is added as a waste to the bar length. This stops the cutters machining when only one end of the bar is held. The amount is normally determined by the distance of the cutters to the infeed clamps. 0-200 This is often how and why a problem offcut is created at the START of the bar – if the maxable is bigger than the chutewidth, there will be a regular need to cut into throwawayChunks
chutewidth The longest offcut length that can fit down the machine chute
throwaway The shortest piece that the machine can reliably eject to the outfeed table. Lengths longer than this need to be pushed down the chute. Therefore the problem offcuts are defined by length >chutewidth and length<throwaway. 130-800 The measurement is taken from the end extremes of the profile The throwaway is determined by the distance between the front rollers on the sawing clamps
Throwaway too short
Photo shows throwaway too short
throwawayChunkSize Maximum size of chunks that a problem offcut piece will be cut into. 25-150 The actual size will depend on how long the offcut actually is – it will be cut into a number equal sized chunks
smallestGrip The smallest offcut piece size that can be gripped and cut at the gripper end of the bar. This is determined by the gripper length and the side / top clamp positions. If the piece is too short, it will flip out of the clamps when you are trying to hold it 20-200 This must not be biger that the chutewidth, as this would lead to an impossible situation where the final gripped offcut could not be disposed of.
useOffcutAtStart Determines whether any offcut should be moved to the start of the bar, rather than deal with it at the gripper end 0 or 1 For all v6 software this should be set to 1
Throwaway Chutewidth and SmallestGrip 0272 Chutewidth 1.jpg

ThrowawayChunk cuts

·        The original software cut the chunks using a square 90 degree cut. However this could lead to a chunk shaped perfectly to fall back into a position in front of the rear rollers, jamming when the pusher moves. This square cut has been changed on later software versions ( to a mitre cut to persuade the piece to fall forwards down the chute.

·        A common problem is a maxable size that needs to be cut into two. This would be defined by maxable>throwawayChunkSize> maxable/2. In this case the chink will be cut in half. If half the chunk size is a problem size, this will happen a lot. In this case reduce the throwawaychunkSize so that maxable gets cut into 3 pieces.

Profile Extra Parameters

On software v 5.14 onwards, profile specific parameters were added to allow you to control the offcut per profile. The params.saw contains the default value, but this will be overwritten with a “PEP”, accessible in the profile settings.

Added peps for profile specific

PEP Parameter Meaning
throwawayChunkSize size of chunks to cut beginning and end waste into
throwaway size that can be safely ejected as a piece
wantHalfTriangle halves the waste triangle on mitre-mitre cuts
trim amount to trim off the start of a bar
smallestGrip smallest size that the saw can safely hold at end of bar

Sample Setups

Machine minable maxable chutewidth throwaway throwawayChunkSize smallestGrip useOffcutAtStart
A2014 90 130 160 240 120 140 1
A2016 90 140 160 240 120 140 1
A2017 90 120 160 240 120 140 1
A2024 90 120 160 240 120 140 1
Z055 140 130 125 250 125 120 1
Z057 100 110 130 320 125 120 1

(post upgrade)

90 110 130 240 125 120 1
F009 (with SY Drive) 90 130 130 320 125 120 1


·        Compare the parameters to similar machine types. If similar but does not seem to be working, ascertain if it is a profile related issue, then reduce the throwawayChunkSize for that profile to ensure it is cut into 3, not 2 – Avoid doing this globally because it will slow the machine down.

·        The relationship between the maxable / minable cut in half and where the rear outfeed roller is can be very important.

·        If there is an issue at the start of the bar on a normal trim cut, it could be because the batch of profile is longer than expected. This can be overcome by modifying the profile standard length or the profile specific trim parameter, both accessible from the profile parameter screen.

Autoflow Offcut Blower

Some Autoflows are fitted with an offcut blower. This was an addition made to help clear the offcut at the gripper end from the table. It is a common problem that the blower has been knocked out of position or is not working, hence offcuts trapped at the end of the bar on the last cut

Throwaway Chutewidth and SmallestGrip 0272 Chutewidth 1.jpg

throwawayMinChunk / throwAwayMaxChunk

v6.4.32.0 January 2020

...This algorithm has proved to fail in practice and in many cases has been switched off by setting the min and max parameters to 100

v6.4.32.0 has added parameters to isolate a certain range of chunk sizes. This was required because the software will always try to cut the throwaway part into similar sizes.

In the case of 1.2m offcut and 2 off 450mm test cuts this looks like

Throwaway 2 cut.png


The waste shifted to the beginning is around 253mm.  The software divides this figure by the throwawayChunkSize (110) and gets a figure of 2 and a bit, therefore makes 2 cuts to ensure all the chunks are <throwawayChunkSize. Annoyingly, for a 253mm long throwaway, dividing it into 3 leaves a chunksize of around 80mm which is just the right size to get trapped in the rear fence.

The min and max parameters set a range of chunks sizes that are banned. If the chunk is within this range, the software will automatically cut and extra cut to avoid this length.

This is the cut pattern with min and max range set to 75-85:

Throwaway Chutewidth and SmallestGrip Image.png

Update v6.4.48.0 September 2020

Further analysis shows the main problem area to be a "maxable" square cut. If the maxable is > chutewidth, then this piece will be cut in two. This is fairly normal on flowlines where maxable=140 and chutewidth=125. This leaves a chunk of 70mm, which is a problem size.

Offcut 70mm Trapped.jpg

To remove a problem cut, the version of software shifts the cut to give a long piece and a very short piece. This is better because these sizes do not get caught in the rear fence. The sizes are calculated by placing the cut at chutewidth-10 millimetres from the end of the piece. This may leave a really short bit (10 - 25 mm at the very beginning of the bar, but this is a more reliable piece size to dispose of.

6.4.48 Before.png


6.4.48 After.png


Standard settings
Machine throwawayMinChunk throwawayMaxChunk
Standard saw, Zx / Flowline 65 85
Ancil saw

See Also

Latest software updates