Throwaway Chutewidth and SmallestGrip

The parameters work together to define the process that happens with the final offcut at the end of a bar when it is too small to be ejected onto the outfeed table. It is surprisingly complicated, particularly on an Autoflow machine where the final piece is gripped.

chutewidth, throwaway, smallestgrip, parameter Throwaway_2_cut.png

Technical Bulletin

...Software version 6.4.29.0 has a new algorithm to control waste. see https://stuga.dokit.app/wiki/Waste_and_trim_cut_improvements_December_2019

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

Problem

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 5.14.2.0 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
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

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 (5.14.2.0) 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
A2014	90	130	160	240	120	140
A2016	90	140	160	240	120	140
A2017	90	120	160	240	120	140
Z055	140	130	125	250	125	120
Z057	100	110	130	320	125	120

Tips

·        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

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

 

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:

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.

To remove a problem cut, the 6.4.48.0 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.

Before

After

Standard settings

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

See Also

Latest software updates

https://stuga.dokit.app/wiki/Waste_and_trim_cut_improvements_December_2019 en none 0

Draft