Saturday, March 28, 2015

Spring Loaded Scriber

I have started to rely more on my CNC mill to scribe outlines for 2d parts.
I typically scribe, band-saw, and then end-mill the profile. 

I made one version but was unhappy with the results and so made this version.

Took a 3/8" solid rod.
A 1/8" carbide bit with a 0.040" end.
Spring and 1/4-20 machine screw.

It needed to be 3/8" so that it would fit into the Sherline collet.

Saturday, March 21, 2015

Snow shovel Rebuild #3

I know its not an invention but when you live in Mi. all your life you become attached to your snow shovel!

 It seems like each repair lasts about a decade, after more than 30 years I have the repair method down.

I really like an aluminum snow shovel and don't need to buy one because I can fix almost anything. 

The business end needs to be steel.

A 2" strip on the underside, .75" on the top side, but the trick is Rivets! I use nice big 5/32 rivets, counter bore the underside so that the hammered end of the rivet is as flush as possible.

Sheline CNC Lathe - Center "Punch"/ Drill for Wood Dowel

I've been doing a lot of turning on my CNC lathe and have become increasingly annoyed with the task of center punching purchased wood dowels.
Two things make the job far more difficult than it should be (or would be if it were steel)
1) Off the shelf dowels are not round, they have become elliptical or worse.
2) No matter how accurately you scribe the center your center punch is going to be deflected (dramatically) by the end grain.

NOTE: A right hand center drill is aiming the wrong way down the spindle so you either have to turn the spindle backwards or get a left hand drill.

The answer is to "machine" the the center "punch"

This is the design prove-out piece
I used  3/8 counter bore fit into a 13/32 piece of brass tube.
13/32 is the ID of the Sherline headstock spindle. It has to spin freely.

This IS a good method!
I don't even support the other end, just visually make it spin true and slowly run the counter bore into the dowel. it only takes a few seconds and is better than even one of those conical center finders.

I liked it so well I decided to make one with bearings and use a center drill.

1/4 x 3/8 x 1/8 RC model bearings. I used my centering tool to create a bearing pack, a 6.5" long 13/32 OD tube, 3/8 ID, the bearings slipped beautifully through.

Wednesday, March 11, 2015

Sherline Mill - Z Axis Reinforcement (Flying Buttress)

For years I have been searching for a retrofit style reinforcement for the flimsy Sherline Z Axis.

Its not flimsy but anyone who has one has probably looked at it and realized that at the upper ends of the travel it couldn't possibly be as stiff as at the bottom. If you run these machines enough you begin to see that the vibrations from machining are resolved mostly in the Z axis.

I run both a hand crank and a CNC version and the real goal here is to develop this idea for the CNC machine.

I have made my 2" increase in Y travel to both of my machines which allows me much greater freedom in mounting work to the table.

I tend to run the 1.25" extension on the spindle mounting all the time. This increases the moment arm between the tool bit and the Z Axis Moment of Inertia.

The box section I fabricated here moves the Moment of Inertia probably the same distance again further from the tool bit BUT increases the overall stiffness.
It would be fantastic to do a comparative FEA on the two versions, I can provide all of CAD data!

I used a 2" x 1.5" x .125" alum. rect. and added 0.125 x 1.5" strips on the sides. The flying buttress is the only way to stiffen the Z Axis because the Z Axis backlash locking lever reaches around and you need good hand access to it.

I had to drill two holes in the Sherline base and two in the steel Z Axis ways.
For the CNC machine I want to make this out of steel but I'm going to try out this one for a while before getting into that.

The more elegant solution would have been 2.25" x 1.5" x 0.125" rect. but that is a rare item indeed.
I'm thinking about a water-jet solid block of alum. too.

Went ahead and made the steel version for the CNC mill.
Should get at least 3 times the stiffness as the alum version.
It looks a little Steampunk but it is extremely stiff!

I added a couple of fasteners to the design to pick up the loose ends.