"Tooling up" - Mill's new belt drive

A faster and more reliable drive

I know it's probably not the most exciting of topics, but there's got to be at least one person out there who finds this interesting. 

So, in the spirit of documenting all I've done, this post is for you, and you know who you are!

Still reading? See, I told you!

Back on track... I had been tinkering with the belt drive conversion idea for sometime, and while I appreciated its advantages, I did not think it was strictly necessary for me at this time.

There were however those few improvements I was looking forward to: 

• much quieter operation 
• increased reliability by bypassing all plastic (yes, plastic) gears used inside the mill’s head 
• more than doubling of the high speed to 4300 rpm, compared the original 2000 rpm

Little Machine Shop belt drive conversion kit #2560

I had seen a few before and after comparisons of noise levels online however, and I was not convinced. 

For one thing, the maximum amount of noise picked up by the microphone depends on the microphone itself, its proximity to the source, what it is attached to, the software running it, and how the gains are set up. Once the sound hits the "red zone", it doesn't matter how much louder things get, the sound just gets cut off.

So, because a sound is pretty loud on video doesn't mean that it is representative of the actual sound level. Indeed, most videos of this kind make it a point to highlight the fact that the belt drive is actually much quieter than it appears to be, and the gears are much louder then they sound on video.

Ultimately this point has to be taken on faith, unless one has seen a live before and after demonstration.

As far as the reliability issue is concerned, I had not had any problems with the mill (yet), although I did crack a plastic 80 tooth gear on the lathe, so I'm familiar with how fragile they can be. 

It is common knowledge among users of these kind of machines, that it is not a matter of if, but a matter of when the plastic head gears will break, so most people are quietly dreading the day when it will happen to them.

Mill's head taken apart revealing the drive train

To minimize this possibility, I have gotten accustomed to taking multiple light passes with my cutting implements. This does increase the time spent machining a part, and should improve the gear’s lifespan, but one can never know for sure.

The problem is not so much that replacement gears might be expensive, but that they require special pullers to take them out, and put them back in. There is also no place I know where one can buy them anymore, so they need to be manufactured at home before the mill (or lathe since they use the same gears) is down for maintenance.

The belt drive is such an improvement in this respect, because it has the ability to slip when overloaded, and replaced when needed without tools.

I didn’t find the speed increase argument compelling at the time, but it was something I wanted so that I could engrave parts in the future, like instrument panels, circuit boards, etc.

What precipitated my purchase, was the sudden availability of the kit online, and since this kit is constantly out of stock, I pounced on it.

What's in the box

Installation was simple, with the only issue being the hole for the spindle locking bar being a bit too tight. I just chucked the bar to the lathe, and turn the business hand down a few thousands. Easy!

The mill now is unbelievably quieter, no screeching plastic noises, just smoothness both in low and high gear.

I am very glad I did the conversion now.

New pulley and bracket in place

DC motor running a new pulley in lieu of the old gear

The new high gear selected

Installation completed

Spindle lock bar in position (used to change cutting implements)

End of spindle tool turned down on the lathe for better fit

Before photo...

... and after.

Another before...

...and after.

By the way, this mod is perfectly compatible with a possible future CNC conversion ;-)

Landing brake - part 2

Time for a brake! (9.0 hrs)

There is something cool about needing a landing brake. It subliminally screams FAST, and it's also going to be the first component of the plane to actually move as it's supposed to. Needless to say, I've been looking forward to this part.

With the landing brake recess cut and glassed, it was time to start manufacturing the actual brake.

I had a few pieces of 3/4” (19 mm) foam in my scrap pile, so I microed them all together to form a landing brake blank.  

Using West System micro to glue the foam pieces to each other

Landing brake blank curing at 72℉

Curing was taking too long, so I fashioned an "EZ bake oven" out of an Aircraft Spruce box.

At 140℉, it cured solid in no time!

Since I cut the slopes of the depression at 45˚, I setup my table-saw at the same angle, and quickly roughed up a matching outline.

This is so much easier than sanding!

Looks menacing already!

The panel fit into its recess a bit loosely, and was in serious need of some top sanding.

This is going to need a lot of sanding!

Following the instructions, I mixed up some 5 min epoxy, and placed small beads into the depression every 3” (7.6 cm) or so, then laid the foam panel back in it.

With the panel firmly attached to the underlaying fiberglass, the sanding started, and went on, and on, and on... you get the idea!

The original 80's landing brake was made out of urethane foam which was very easily sanded, but there were later issues with its strength, so the move was made by RAF to the much stronger, but harder to sand blue foam.

Polishing my cabinet making skills!

The two shims prevented the forward lip from dipping into the deeper part of the recess, under pressure.

Eventually the tough foam was sanded into submission, and a pretty nice brake started to emerge.

Gray tape was added once the final shape was achieved

This is where I deviated slightly from the plans, and took a different but proven detour.

Borrowing from Beasley’s experience, I used modeling clay to fill in the gap that had been created, so that the outer BID layup would bridge across it without any dips.

The clay will be removed before glassing the inside part of the brake.

I wish I could take credit for this smart idea, but it was Beasley's.

I think I've done this once before... in kindergarden!

Looks like a square blueberry pie, crust and all!

No need to be too precise here, somewhat flat will do.

Gap bridged, we are ready for glassing.

Last thing left to do was prepping the work area for 3 simple flat plies of BID.

When the epoxy started flying, I ended up needing all this protection.

I chose to reuse a small piece of BID, but I would do it differently now, and go with a full BID piece, since the scrap left a minute bump on the finished surface that could have been avoided. This will be fixed with the final outer coating, but I will try not to do this again on the exterior surfaces.

Reusing scrap bid. Bad idea on outside surfaces!

All three plies curing

You can't see it, but there's a tiny ridge where the scrap overlaps the rest of the first ply.

Landing brake - part 1

Creating the depression (20.0 hrs)

The landing brake will be housed in a depression carved into the bottom of the fuselage.

Like plastic surgery, it all starts with a sharp cutting implement, and a lot of hope for the end result. 

"Nip and Tuck"

Fiberglass did not stick to the strategically positioned packing tape below it

As much as I tried holding the cutter at the 45˚ by hand, I kept steepening the angle for some reason, so I decided to rig something up to help myself.

Cutting a slot at 45˚

This worked very well indeed, and the plywood panel fit nice and snug into the slot at the required angle.

The hinge will attach to the plywood, after it gets trimmed down

Because I still needed to cut the actuator slot into the fuselage floor, I tried the “carpenter square” method again, with equally good results.

Vertical milling

And voilà,  a landing brake actuator hole!

The plans call for carving a 0.5” to 0.6” depression into the foam. As I did in the past, I used the router to clear up the foam in a consistent matter.

A "depressing" job

Clearing the foam

Edges sloped at 45˚

Up until this point everything went pretty fast, but it only took one dumb decision to deviate from the plans sequence of events, to put the stop to that!

I thought that it would be simpler to drill and tap the aluminum blocks before attaching them to the fuselage. While I was right about that, I didn’t anticipate the amount of work, and headaches this would create for me later.

Aluminum blocks erroneously tapped before installation (don't you do that!)

Aluminum blocks epoxied to the plywood (swimming against the current now!)

Needless to say, I should have followed the plans. What was I thinking?

To prevent micro-slurry from getting into the threaded holes I tapped into the blocks, and that should not have been there in the first place, I had to make something to plug them temporarily. So, I shortened some bolts I had, and cut slot into them to allow me to remove them later with a screwdriver.

Trying to dig myself out of the hole

This ought to keep the evil micro at bay

After carving more foam to clear the actuator brackets, I microed the plywood into the slot I had carved, and went to bed.

Plywood, aluminum blocks, and headless bolts microed in place

Done for the day

The next morning, I prepped the fuselage for glassing by taping around the depression, and putting dry micro into every sharp corner.

Ready for surgery

Smoothing all corners with dry-micro

The plans require 2 full plies of BID, plus a third smaller ply over the hinge section only. I elected to lay the smaller ply first, so that I would have a smoother transition without having to use extra peel-ply across the layup.

Reinforcement layup

2 full size layups

All 3 plies in place

Lastly, I trimmed the fiberglass all around the perimeter, and peel-plied over it.

Edges trimmed, and peel-plied

A better angle