Doin' my best just to change my yesterday, Then I won't have no more errors of my way.

by Ivan Hamilton 4/21/2008 12:53:00 PM

Spin motor left, spin motor right. Easy enough. The next step is to get positional feedback by mounting an encoder on the motor shaft. Sounds easy enough, doesn't it? But since my motors don't have a shaft on either end, I'll need to add an extension.

Luckily someone much better than me has already done this, and put nice instructions on the web. How hard could it be? It would also be my first real piece of work on the new mill.

What I needed to do What I did
Machine flat the raised area where the encoder will mount. Fixed the endplate to the mill table on top of only two standoffs.
The plate wasn't flat, and halfway thru gouged below the non-raised face.
Refix the workpiece using 3 points and machine flat (hoping the circular valley won't matter).
Drill a slighly oversize hole in the center of the end plate. Drill an off center hole, and then roughly open the hole in the direction of where the hole should be.
Drill a hole straight down the center of the motor shaft. Drill a hole angled down the center of the motor shaft.
Machine a 4mm bar for the shaft extention. Machine a 3.9mm bar which is too small for the encoder wheel to grip.
Machine a new 4mm bar, but thin up one end so it can sit straight in the angled hole.
Add glue and insert shaft extension until the glue rises to just ooze a fillet above the end of the rotor shaft. Add too much glue before inserting shaft extension.
Dab at glue with paper towel to remove glue until shaft extension can be inserted without glue flowing over the bearing.
 Drill and tap 2 x M2.5 holes for mounting screws. Don't check the screw size. Eyeball the screw and match against the smallest tap in your set.
Drill and tap 2 x M3.0 holes for mounting screws. Scratch your head when the M2.5 screws just fall out.
Bore out the encoder board and base to 3mm to fit M3.0 screws.
Realise you don't have suitable M3.0 screws.
You have to go out to buy M3.0 screws, so you may as well buy a M2.5 tap and use the right screws.
Abandon your 2 x M3.0 holes.
Drill and tap 2 x M2.5 holes for mounting screws.

It didn't go completely smoothly, but no fatal mistakes were made. A couple of cubic millimetres of material were removed that didn't need too... and a bit of extra glue.

At the end of the day... I'm fairly happy with the results.

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Mechanics | Pragmatism

Backlash Blues

by Ivan Hamilton 4/16/2008 10:59:00 AM

I've got my mill now, and I've had a little play with it.

One of the things I've noticed is the amount of play in the hand-wheels before they move the table. After turning in one direction, the hand-wheel will move back an indicated 0.2mm before they engage again. This means if you're using the markings on the wheels alone, you may wobble about by 0.2mm.

I took a quick measure of the change in distance between the bearing block and the wheel mount during a left to right transition: 0.1mm. The details of how the screw is mounted to the table is hidden a little, so I disassembled it to get a good look.

Screw (with pin), first thrust bearing, the bearing mount, second thrust bearing and hand-wheel mount

It's pretty easy to see where some slack in the system comes from... there is nothing holding this assembly together tightly. It relies on the placement of the pin and pin bores (it's important to keep in mind here that this is a economy Chinese machine, and not high precision equipment).

With the screw released from the table, I measured the movement of the screw against its "nut" on the saddle: 0.1mm.

0.1mm in the nut + 0.1mm in the bearing mount = 0.2mm total.

At the moment I'm not looking to eliminate this movement. I'm just looking to identify it... I just had a wild realization. In talking fractions of a millimeter (mm), it makes sense to use the next prefix - micrometer (µm). I've never dealt with such little units before. 0.2mm=200µm. Microns baby... microns. We're talking about two and a half times the width of an average human hair.

Maybe I'll just shim it with some average human hair...

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Mechanics | Pragmatism

My mill mach' brings all the boys to the yard...

by Ivan Hamilton 4/1/2008 3:36:00 PM

I finally did it. I've been thinking and looking and scheming for over 12 months. And here it is...

Now I just need to work out how to use it. If you're looking for a machine like this, I can highly recommend Titan Machinery. Stuart from Titan has been very helpful, and continues to be so.

I'd looked at mini-mills like the Sieg Super X3 series, but they have only 300mm x 160mm x 350mm travel and are priced around $2200.

For only a little more, I got one capable of 500mm x 200mm x 450mm. Oh, and this one had a stand, vice, drill chuck & arbour, face cutter, clamp kit, lamp, collets and collet chuck, and chip tray (several hundred dollars to buy elsewhere).

This is the largest machine I found before they become floor standing and suddenly 700kg! Without a permanent workshop to place it, I need something a little easier to move. At about 350kg total, this machine is "man-handleable" when disassembled.

What next? Well, I've got the guitar, I just don't have any strings yet... and sheet music is a long way off. Huh? I have a $30 power drill... I don't mind cheap power drills since they take a fair bit of abuse and I consider them a consumable item. When dragging them around, they're eventually going to get destroyed (full of sand, dropped from height onto concrete, burnt out by stupid use, etc). The small collection of drill bits I have probably cost 10 times what the drill cost. Good drill bits make all the difference when drilling solid material, and will out last cheap ones many times over. I assume milling cutters will be the same; there will be many cheaper alternatives available... but in the end a good quality set is well worth it. But cheapies are good to practise with.

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Without tools he is nothing, with tools he is all.

by Ivan Hamilton 2/7/2008 5:20:00 PM

It's part of a man's journey through life to accumalate of tools. Of course, you need somewhere to store such tools...  

A suitable toolbox is a important as the tools it will hold. I've got two main toolboxes, one small and one large one. They've grown a lot, with large tools in the small and small tools in large... it was time to empty all their contents and refile them.

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"My inner nerd can beat up your inner nerd."

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