An Interesting Tool to Use

[KeithB]

I recently designed and built a simple fixture that will be used to hold tubing sections at a specific angle for tack welding. The product is a tailwheel pivot that we make for one of our principal customers. It is similar to a pivot they already sell, but the angle is different and thus requires a different fixture.

We make the tube pieces from 4130 steel tubing - the upright piece is 1.25" OD/1.00" ID/2" long, and the angled piece is .875" OD/.625" ID/2" shortest length. The pieces get cut off, the ID is drilled and reamed, and the short piece gets a fishmouth milled into the end with a 1.25" endmill.

The fixture consists of three principal pieces, a base, a vertical pin, and a notched block. The base is a simple block of aluminum with a few simple features, the vertical pin is a piece of 1" dia cold rolled steel, both required basic milling machine and lathe work, nothing remarkable.

The notched block had to have a slot of a specific width cut at a specific angle (33 degrees). The best and most accurate way to do that is to use a sine bar or sine plate. A sine bar/plate is a tool that consists of a bar or plate with two round bars mounted underneath at a specific center distance. By putting one roll on a reference surface and raising up the other a specific height a specific angle is created between the reference surface and the top of the bar/plate.

I used a 6" sine plate, with a 5" center distance between the rolls. In order to get a 33 degree angle I had to use the sine function. The center distance is the hypotenuse, so the height needed to raise up one end is the sine of the angle multiplied by the center distance.

Height = sin(desired angle) * center distance

In my case of 33 degrees:

Height = sin(33deg) * 5" = .5446 * 5" = 2.723"

I machined a block to the right height rather than use a stack of gauge blocks.

The sine plate was located square with the table axes by using a dial indicator, and then the pre-machined block was bolted to the sine plate surface and checked with the indicator. One end of the plate was raised up and set on the height block, and an additional clamp was used to keep everything secured.

You can see the layout dye and lines I scribed on the block, but all measurements were made with micrometers to keep the slot in the middle of the block.

The end result lined up the tubing pieces perfectly, sorry I didn't get a photo of that. At least I got a good shot of the finished fixture.

 

[smokeywolf]

Keith, what was the purpose of milling out the underside (at the corresponding angle) of the angle fixture?

Also, nice sine plate. Always wanted an articulating sine plate but never came across a job that would justify the purchase.

Fixture designing and building is fun. I miss the smell of Dykem.

 

[Gary]

Great stuff Keith, I always enjoy your posts.

 

[KeithB]

Smokey, after I cut the top slot as shown, I flipped it over and put it in my regular 6" machine vise to mill out the underside. The reason I needed to mill it out was to allow a small C-clamp to be used to clamp the angled tube in place for tacking. The vertical tube is held in place with a 1/4-20 cap screw and a couple of 1-1/4" fender washers. The purchaser has a shop full of C-clamps and Vise grips, so I didn't supply those and thus no picture of the tube pieces being clamped in place.

I've had a sine bar for a long time but had to make a couple pieces using a sine plate so I just bought one. It was a little over $100 from Ebay. My first job paid for the tool, the second one paid me for my labor. I feel like I broke even and now I have it to use as long as necessary.

I used aluminum for the base and angled block to keep frog eyes from sticking, and steel for the center post to keep the threads from stripping out.

It's just the rubbing alcohol in the Dykem, not nearly as pleasant as the smell of a good bourbon or cognac.

Didn't know how many hobby machinists here were familiar with a sine plate or what ideas it might spark.

 

[smokeywolf]

What I've usually done for one-off jobs like that is clamp a precision grinding vise in the Kurt, set the angle with an angle block and clamp the part in the grinding vise. That scenario has its limitations and is certainly not as sure as using a sine plate, but didn't always have a sine plate immediately available.

 

[KeithB]

Seems like a good work around. Too bad we don't live close, I'd loan you my sine plate if you'd let me borrow your grinding vise.

 

[Intheshop]

Keith,we use modified V blocks mainly cause they're cheap but they can reference off more than one plane...... and they're cheap.BW

 

[KeithB]

Yeah, I've got a sine bar, a set of 30-60-90 and 45-45-90 ground angle blocks and a set of angle blocks in 1 degree increments, but for some things a sine plate is just the ticket. Next I plan to get a small, low vise to clamp to the top. I just realized I can also clamp my C5 collet holder to the top. More versatility is a good thing.

 

[smokeywolf]

Bought my precision grinding vise while still in my apprenticeship. Not a name brand like Suburban, but maybe one step up from Enco. If I remember correctly, we got about a dozen guys together in the shop, bought them while they were on a sale, then got the retailer to knock off another 10%.
That little vise has seen a lot more time on a mill than on a surface grinder and has saved me a lot of hours in set-up time.

Nowhere does the old adage of, "time is money" apply more than in the machine shop. One of the "old timers" in the MGM Machine Shop, an old Danish Merchant Marine ships machinist, taught me, "good set-up, equals good parts". While I've always followed that precept, too much time spent on set-up can eat up profits quickly. Much of my tooling purchases have been driven by this.

 

[KeithB]

I'll agree with your old timer friend and add that good setups are even more important when you are trying to bulk-produce something. I spend a lot of time trying to make tooling and fixturing that is not only accurate but also quick and simple to use. It helps that I can control most of the job processing, from part design to raw material selection to fixture design. Another thing that helps make for faster setups and smoother work flow is to have a process sheet for each job. Every time we do a new job I generate a spreadsheet to list the tooling, operations/steps, CNC program numbers, work holding methods, etc. I include notes and photos of setups that are more complicated than just using a vise or 3 jaw chuck. The next time we get that job we can pull out the file and know exactly what to do and how to do it every step of the way. We can also make sure we have all the proper consumable tooling on hand, or order it when we don't in time not to delay the job.

Not much different than the extensive notes on guns and loads that I'm sure many of the folks here seem to keep.

 

[Pistolero]

This illuminates one of the points I make to friends when they talk about "how much would it cost to
make this?". How you will make something depends on how many you will make. As you plan
a larger product run, you can afford better tooling, jigs and fixtures for manufacturing. BUT, the
time and materials cost is front loaded onto the production run. Making a fixture that costs $100
and takes a couple of hours to make a production run of two items is not likely to work well economicly,
but if the production run is 100 or 1000 that makes all the sense in the world.

Clearly the intent is for a fairly large production run, probably much more than 100 units.

Bill