Silhouette Curio-sity

Here we have our general purpose die cutter, stencil, etching, marking machine.

Silhouette Curio. Die cutter and etching machine.

By all marks a reliable, accurate, and best of all inexpensive piece of equipment.  Pair it up with their Silhouette Studio Designer Edition, and you have a platform to go from CAD to anything that requires surface markup.  We are constantly pushing the boundaries of what this machine can do.

Now, the machine only has one tiny flaw and it is strictly associated with how we are using it.  No one (at least in their right mind) would be trying to create cut elements down to .001″ accuracy from a unit available from a craft store, but we are.  To achieve this,the only part we had to modify was the deck hold downs.

Silhouette Curio original build deck with quick release snaps.

The original design is beautiful and functional with a distinct usage pattern in mind.  It was setup for the user to be able to quick change parts from the deck, simply undo the snaps and replace.  Great concept, to be able to setup or work material while the unit is busy and then quick swap.

Where the quick swap gets us into trouble is the amount of play they require.  Now while cutting a stencil of your name you won’t notice .050″ shift in the pattern, but an optical encoder will.

So this mod focuses replacing the snaps with hold down bolts.  While we may lose some efficiency in the quick swap, we get a massive boost in accuracy when cutting small dimension structures.


First up we need to measure the build deck pad snap holes, and select an appropriate size of through bolt.

Silhouette Curio build deck pad hold down hole. Measured to 0.195″.

The build deck pad hole(s) measured 0.195″, so a #10 hex bolt at 0.180″ average shaft diameter gives us 0.015″ of play for mounting.

#10 x 5/8th’s hex head bolt for build deck hold down.

A 5/8th’s length bolt will give plenty of stock to work with for any size trimming required without excessive waste.


Next task is to drill the through holes into the deck that line up with the quick snap hold down posts.

Close up of hold down snap and left alignment post.

Fortunately the hold down snaps are designed to be replaced, so we can make this mod and revert to the original configuration if desired.

Sharpie strike marks aligned with hold down snap post.

With the snap hold down in place, strike alignment marks freehand with a sharpie or pencil.  Given the free floating nature of the build boards, perfect hole alignment isn’t required…. but getting close helps.

Center mark for through bolt hole.

Remove the hold down snap.  Then use a straight edge to form a cross center mark based on your outside markings.  This will be the drill point for the through bolts. Repeat this for all four hold down points.

Layout of drill bits and through bolts. 3/32nd’s (0.0937″) pilot hole bit. 3/16th’s (0.1875″) primary hole bit. #10 x 5/8th’s hex head through bolts and nuts.

Since plastic surfaces are slippery in general it is advisable to select a small drill bit to create a pilot hole.  This will minimize “walking” when drilling the primary hole.  Went one step further by using a spring loaded punch to dimple the center mark for the pilot hole.

3/16th’s through hole, and #10 x 5/8th’s hold down bolt.

Drill holes on all four marks and you’re ready to trim the bolts.


Insert only the upper left bolt, along with one build pad spacer.  Lay a flat edge across the alignment post and against the side of the through bolt.  Use a sharpie to mark where the flat meets the bolt, this will be trim height.  Must be done to insure that all bolts clear the inside of the machine.

Marking through bolt for height trimming.
Measure of strike marks results in bolt shaft length 0.435″.

Measure and strike all four bolts for cutting to height.  If you don’t want to trim things you can probably get away with 1/2″ length bolts to start, but has not been tested.

Using a machinist vice and hack saw, trim all four bolts to the strike marks.  It is handy to put one nut on before cutting, so if threads get damaged you can back the nut off to straighten.

Trimmed bolt with nut. Inserted and tightened to build pad.

Last item is the head height of the bolts.

The two hold downs along the left side of the board are situated above a honeycomb structure.  This provides excellent clearance for the stock bolt heads.

Board underside honeycomb structure and bolt head clearance.

Unfortunately, beneath the right hand side of the board hold downs is where several motion components travel.

Motion component travel lanes, showing new bolt head obstruction.

To fix this we need to shave the bolt heads to equal or less than the well depth.  This conveniently is also the same thickness as the solid part of the quick snap hold down, so measuring is easy.  The resulting bolt head should be 0.045″ +/- 0.005″.

Trimmed #10 bolt with nuts for mounting in 3 jaw lathe. Note keep space between nuts so they don’t jam during clamping and cutting operations.
Facing cuts on #10 bolt head, trimming to 0.045″ height.
Trimmed right hand bolt head, with normal and quick snap for comparison.
Trimmed bolt heads showing clear way for movement components.

If you don’t have access to a lathe of grinder, you can probably establish sufficient precision with just the two left hold down bolts and right quick snaps.


Mod is complete, tested for freedom of movement and ready for use.

Silhouette Curio build deck with finished bolt down modifications.

Go to main project page

Ear Mold Container

First of all.. ew.. Ear Mold?

Actually it’s not what you think, and technically it’s an impression with the ear itself being the mold.  Which would be a good topic for later discussion.

So here’s the project.. Create a pocket sized container for a pair of custom fit hearing protection plugs.  It needs to keep them together, yet with separate compartments for sanitary purposes.  Small and light weight, fitting easily in a shirt pocket.

Left and right custom hearing protection.

Quick measurement allowing for finger clearance yielded for each pocket:

  • 1.000″ wide
  • 1.500″ long
  • 0.625″ deep
1.000″w x 1.500″h x 0.625″d pocket requirements.

To start off with, you really only need to design half a box and mirror it over.  Here we see the exterior plan form with edges rounded for comfort.

Half container plan form with rounded edges

Then create lines set 0.0625″ (1/16th) in from the exterior plan to create the well and side walls. From that generate an extrusion 0.1250″ (1/8th) shorter than the main box, and subtract leaving the final well.

Hollowed structure with 0.0625″ (1/16th) side walls and 0.6250″ depth. Creating a 0.1250″ (1/8th) thick floor.

Take the formed box structure and mirror it along the center of the separating wall.  The result will be the final box form with the required two wells.

First structure mirrored then added together for final box result.

Add the mirrored sides together leaving the final product ready for production.

Final well box design, ready for printing.

Off to the printer we go.

.STL sliced, checked and ready for printing.
Print complete. Run time 40 minutes.
Well box checked for sizing and fit with ear molds.

Now that we have a box that fits the items, it’s on to the lid.  Nothing truly special here, just a simple 0.0625″ (1/16th) cap with tangs to grip the interior wall surfaces.

Underside of cap design to highlight grip tangs.
.STL checked, sliced, and ready for printing.
Printed well box cap ready for checking. Run time 10 minutes.

Now that all our pieces are off the printer, time to check for fit and last minute changes.

Box, cap, and ear molds.

Cap fits snug with the tangs keeping a firm grip.  Subjected container to shaking while holding the sides and facing down, simulating shocks with ear molds impacting the cap interior.  Cap did not fail under load.

Completed container ready for delivery.

Designed, printed, tested and ready for delivery in just under two hours.  No surface treatments added due to possible reactivity and health concerns with ear mold contact.  Client satisfied with results and will report back with any issues or desired changes.

Go to original project page

Fat Gecko Fix

So here’s a project that came in the door with a 24 hour turn around time.  It’s a Delkin Fat Gecko suction cup mount rigged for iPad holding.  Problem, the turn screw closest to the iPad holder had become frozen and would not tighten securely.

Delkin Fat Gecko iPad mount, in standard position of use.

Now based on the position that it is usually mounted as you can see above, most of the stress is torsional.  Also this unit is subjected to near continuous vibration, so requires regular tightening.

Failed turn screw and knob.

Combine regular tightening with a fixed position and the result is thread wear, spalling, freeze up, and finally failure.

While not a complete failure of the turn screw, it was pretty close and required significant working to release.

Required channel locks to loosen for release of rest of unit.

Once freed from the rest of the unit, the threaded side was clamped into a machinist vice for complete removal.  This required careful application of force, as there was a significant risk to the remaining internal threading.

Secured head in machinist vice, and channel locks required for complete removal.

Finally free for layout and component inspection.

Layout of components.

As you will see below there was thread destruction about .18″ in from the screw tip.

Inboard and outboard turn screws, showing thread damage on frozen item.

Luckily the extraction did only minor damage to the internal threads on the head.

Frozen screw base, threads with evidence of spalling and minor damage from removal.

Since a knob of that type using 1/4″ x 28 threading is not a common hardware store item, the first choice was to refresh the threads.  This was also driven by the short 24 hour turn around requirement.

Attempted thread refresh with 1/4″ x 28 die.

Cutting damaged threads requires careful attention and patience.  Slowly lubricating and cutting a 1/4 to 1/2 turn at a time, with chip clearing along the way.

Lubricate. Twist on. Cut a half turn. Twist off. Repeat.

Unfortunately, things don’t always work out as you plan.  The result was the removal of to much material from the threads, creating a loose fit and low clamping force.  Also the stress popped the shaft from the knob head, revealing it to be a 1/4″ x 28 hex drive bolt.

Knob and hex drive screw after thread refresh failure.

Now what is common to the local suppliers are 1/4″ x 28 range hex head bolts.  When compared to the original, a 1/2″ length bolt would give sufficient clamping force without bottoming out.

Speaking of bottoming out, based on a cursory inspection it may have played a role in the original bolt failure as well.

Comparison 1/4″ x 28-1/2″ hex bolt for comparison with undamaged screw.

Now with a proper bolt, we need a way for it to be tightened by hand.  Can’t tell the client to carry around a wrench, so we need to make a knob to fit from scratch.  This also opened an opportunity for a better fitting solution, since the client expressed a desire for a lower profile on the unit.

Surprisingly enough, there wasn’t a 1/4″ hex screw / knob model in our project collection.  It’s a simple enough object, so the total modelling time was negligible.  Started with a basic round for draft printing speed, test fitting of bolt and head spacing.

1/4″ bolt hex head knob model.
.STL processed and ready for printing.
Draft printed 1/4″ hex head bolt knob.

With the clearances checked, time to move on to a more user friendly form.  For this we added indents to the circular construct, creating leverage for tightening.

1/4″ hex head bolt knob, with finger grip indents.
.STL processed for printing.
1/4″ hex head bolt knob, printed but not surface finished.

Once printing was completed, staged assembly of the replacement parts for comparison.  Added a nylon washer between bottom of knob and top of head casing, easing tightening and reducing surface wear.

Replacement knobs for comparison.
New assembly layout, showing knob height profile reduction.
Arm assembly showing knob height profile.
Finished assembly and layout in standard use position.

Also added a healthy dosage of grease to the screws prior to assembly for life extension.

Client declined surface finishing of the knobs as the tactile nature of the rough print provided better grip surface.

Unit returned to client ahead of schedule and received positive initial satisfaction of results.  Awaiting testing and feedback for any desired changes.

Side notes :

While this was the best solution given the time constraints, it wasn’t what could be considered the best solution for longevity.  The shorter bolt length could exaggerate the internal thread issues, leading to freezing failure again.   Optimally we would have preferred a machined insert that passed completely through the head, creating a greater clamping force and allowing replacement as needed.  Processing would have exceeded the return to service deadline, and was put on hold for client consideration.

Go to Original Project Page

Lathe Trick Out (overview)

(Overview)

So here is our workhorse bench top lathe.

Central Machine Tools (Harbor Freight) 33684 7″ x 10″ lathe.

By every stretch a capable manual project machine, durable and in the right hands very accurate.

So why would we want to mess around with a good thing?

Beyond an incessant need to tinker with things, we want to increase it’s utilization.

The only way to achieve this is with automation controls, or CNC as it’s known.

This gets us the following;

  • Flexibility of cut types and movement.
  • Increased precision and repetition.
  • Lower machinist tasking and interaction.

The machine operator or machinist is the great brain of any manual tool.  As diligent and precise as they can be, they are still human.  Two parts made by the same person on the same machine can end up having subtle variations.  CNC greatly reduces these variations, but still requires the accurate monitoring of the machinist.  So instead of replacing the brain, we want to give it time to do other things like monitor the mill at the same time.

Now we have a great tool but when the machinist doesn’t have hands on it, it’s a paper weight.  Hovering over a spinning piece of metal, hands at the ready to push buttons and twist knobs.  Insanely time consuming, and yet necessary to achieve a good finished product.  This works great for a one off article, but will drive the machinist batty making ten more just like it. Still we want to retain the basic abilities of our great tool.

That brings us to the core requirements of this project;

  1. Retain the basic manual abilities of the lathe.
  2. Enable CNC level control of all functions.
  3. No downtime during conversion.

So what does all this mean?  Where there’s a dial and switch, there will still be a dial and switch.  The computer’s control will have to overlay on the human input devices.  We can’t take the unit out of service at all during the conversion.

Whew!  That sounds like a lot of work to achieve something you could buy off the shelf?

Fair point.. but learning by doing is way more fun.

Take me to the main page.

Cutting Board Conundrum pt2

So we have our cutting board after 5 days of clamped cure time, and 5 days of free air rest.  We have a stable bond across the seam and appears to be a successful repair.

Cured and rested board showing repaired seam.

Yet as we can see the warp is still there along with the hard plastic feet.  So we have to move on to relieving the impact stress to the board.

Hard plastic feet and warp as seen across flat surface.

Choice of material is clear rubber bumpers.  This will even out the stance of the board on flat surfaces, and dissipate impact stress.

Hard plastic feet removed, rubber bumper replacements with screws.
Select drill bit for pilot hole, compare to screw ensuring it is not bigger than threads.
Insert into drill chuck to be equal or less than the length of the screws.
If drill bit is still too long, use a nut or washers to create a drill stop.
Mark center points and drill to depth.
Finished bumper installation. Even load distribution to all corners and center line support.

Repairs completed and delivered to client with satisfactory results.

Previous : Cutting Board Conundrum

Cutting Board Conundrum

So here’s what we have.

Client presented a damaged wooden cutting board.

Now you may be thinking why bother, spend the $20 and buy a new one.  Well this particular board is circa the late 1960’s, and has sentimental value to the owner and a repair was desired.

Now a simple repair could have been aesthetically acceptable, but client desired it to remain functional.  So a lasting solution was required.

Identifying points of failure was key to the repair.

First was the seam in the grain that failed.  With time and washing a pronounced warp had occurred, resulting in a 2 points of contact situation.

2 points of contact on left and right of photo

This paired with the original hard plastic feet, allowed impact stress to concentrate along the weakest point.  Thus a crack was born.

Fortunately the face was fairly uniform allowing for alignment and mating without much problem.  Unfortunately this would allow a weak spot to remain unless some form of reinforcement was applied.

A biscuit joint while strong would have affected the mating surfaces, and potentially compromising the adjacent grain sections.  Some form of underside strapping could have been effective, but was discarded due to the aesthetic considerations.

The solution was a grid of 1/16th inch holes cross drilled into the mating surfaces to a depth of 1/4 inch, and strong glue with food safe properties.  This would allow the glue to bridge adjacent layers without substantial weakening of their structure.

Hole spacing line strikes 1/4″ from top surface, and 3/16″ from bottom with 1″ parallel holes. Additional holes in the middle of each 1″ segment.

Once the holes are prepared and any stray bits of wood are removed, it’s time to bring things together.

Apply glue to mating surfaces and massage into the surface. Allow penetration into cross drilled holes, continue massaging until no more bubbles appear.
Uniform surfaces, ready for mating.
Mate pieces, and clamp so as to apply pressure across the surfaces to be joined. Excess glue will squeeze out every direction, so wipe and remove carefully with the grain and not across it.

Cure time according to instructions is 24 hours, but it is always better to allow as long as possible.  In this case the board was set aside and allowed to cure clamped for 5 days, then rested for another 5 days before work continued.

Next : Cutting Board Conundrum pt2