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Production Strategies on a Home Built Machine

I cut a lot of parts on my home built machines.  These machines were never designed for production work, so I have developed strategies to get the most productivity out of my work.  My goals are to get the best yield out of my material, have the shortest run times, spend the least time babysitting the machine, minimize tool breakage and get the highest quality parts.  This post is primarily focused on routers, but some of it also applies to laser cutters and other machines.

Modern professional, production machines will have vacuum hold downs, tool changers and automated clamping, etc.  This post is about optimizing basic machines.  A lot of this is obvious to many people, but recently I have seen some videos where I saw poorer strategies and even examples where part quality is going to be hurt.

Don’t Break the Tools.

For me, as a hobbiest, my time is cheap compared tool costs.  The first priority is preventing tool breakage.  I usually run with a 1/16″ dia. 1/2″ cut length carbide bit.  This minimizes material loss.  These babies are brittle.  One mistake and it will break.  With that said I have cut continuously in Acrylic for 6-10 hours with one bit.  When cutting out parts, my number one cause of breakage is getting caught on a loose part or scrap.  I design my cutting to prevent pieces the might break the bit from flying around.

Analyze The Part.

The first thing I do is look over the part to see the issues I might face during while cutting.  The first issue I see is the large oval internal piece.  This piece will come loose and is big enough to cause problems.  It might try to jump out of the hole and catch on the tool or it could land somewhere where the tool will come down later.  The smaller circles won’t be a problem.  The cooling blower on the spindle will whisk those away.  The small slot could be a problem.  Long aspect ratio, small cutouts often start to fly away, but get hung up if they tip on the way out.  If a rapid move happens to cross this, it could break the bit.  I would probably address this by choosing a rapid move height of about a material thickness above the surface.  Maybe a little higher if the slot is longer.  An excessively  large rapid move gap will seriously waste time, so I want to choose this carefully.

Keeping things together.

There are several methods to keeps parts from flying around.  One popular method, if your software supports it, are “tabs”.  These are small uncut or partially cut areas that are left behind.  Ramped tabs like I show above are a lot faster because they do not require the move to stop and retract at each tab.  This method works well on parts like wood that will probably get cleaned up and sanded later.  On some parts like aluminum or plastic, it may not give you the even finish you want.  The second method I use when the cut will require multiple passes is to leave the final pass to later.  All parts are cut, unattended, down to a small remaining amount.  Then all parts are cut out with me there.  This can often be done at very rapid rate if not much material is left.  I usually use a soft wooden, hand held  “chicken stick” to hold the parts down during the cut.

Clamping

Clamping can be a challenge on large sheets.  You can clamp from the edges but the center might bow up a little.  This gets worse as the parts are removed and only a thin web of material remains.  Bowing causes two problems, you can get chattering of the material which impacts cut quality and your zero Z point is not consistent.  I use two strategies to deal with this.  If all the cuts are through and a little Z variance is not a problem, I try to cut out parts from the center and work my way out.  This keeps a stronger path of material to the clamps.

If I have blind pockets to cut and the depth is critical, the Z need to be accurate.  In this case, I will usually run the though hole toolpath first, then add a few wood screws through the material and into the spoil board in the central areas of the material.  Make sure your rapid Z will clear the screw heads or the rapid path avoids the screws.

Cut Order.

Obviously you want to cut all internal part holes and features before you cut out the part because the part needs to be held firmly in place.  I chose to not cut any parts out until all internal features on all parts are done.  This keeps the material ridged as long as possible.  This applies to laser cutters as well.  People are not as conscious of cut order because parts are less likely to move, but on really small parts on thin material the assist air or exhaust blower can move the parts a little.  I see cutouts before internal cuts all the time on videos and I can see the parts move.

I optimize my cut order to minimize my babysitting time.  I cut all large internal part features first and monitor that.  I then combine a lot of unattended toolpaths.  First is the cutout of all small internal feature.  Next I cut any blind pockets.  Next, I cutout all the parts almost through.  This is generally the longest run.  The machine will stop and wait for me.  I then completely cutout all the parts working from the center our while watching the machine to prevent problems.  I will use my “chicken stick” on parts I think might jump out.

Cut Speed.

Don’t be afraid to raise the cutting feedrates.  Most tools are optimized for certain chip sizes and speeds.  You are not doing the tool any favors by running it slowly.  If the tool cannot make decent chips, it will run a lot hotter and will dull and fail sooner.  You need to experiment with speeds to get the highest reliable speed.  Home built machines are not perfect and things like runout (wobble on the tool) and tram (Z out of square) problems might come into effect before ideal speed is reached.  With high speed router spindles consist single flute tools.  Don’t be temped by cool looking 4+ flute tools.  They are more expensive and will give you a worst cut and will fail faster.

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