Backwards Bandsaw Teeth

Today I decided to swap out the default blade that came with my metal cutting bandsaw in favour of a bi-metal blade which is a recommended upgrade. Much to my dismay, when I went to install it the direction of the teeth was backwards. How could the vendor do this to me when I bought both at the same time? ARRGH!

A bit of online research later, I found a saw vendor’s note about how you can just flex the things and turn them “inside out” and thus change the direction of the teeth… I am very glad I did the look up before I called the store to announce my ignorance.

Metrology Monday: Sine Bar

What is a Sine Bar For?

I consider this sine bar to be the most exotic measurement tool I have. I bought it mostly for fun. A sine bar consists of two cylinders of the same diameter fixed with their centers a known distance apart. The top of the connecting bar is parallel to the line between the two centers. All this done with as much precision as you are willing to pay for.

What the bar is used for is to “construct” precise angles between the bar surface and the surface the bar is resting on, typically a surface plate. Given the desired angle, one does the appropriate calculations (hence the sine name) to get vertical displacement for one end and builds that height out of gauge blocks.

Here as an arbitrary example, is a setup to get an angle of 32 degrees, 16 minutes and 27 seconds. Reference to an online calculator produced a displacement of 2.670″.

I called this tool exotic because it is difficult to conceive of a circumstance where I would actually need to measure to set up an angle this precise. I can use it as part of a machining setup or to check something like my engineer’s protractor for accuracy. I expect that an experienced machinist has more uses for one so who knows.

Alternatives

Budget sine bars cost less than $50CDN new so it wouldn’t break the bank if you decide you needed one. There are lots of protractor variants that are probably more practical for most jobs.

Options

The “sine tool” family includes plates and vises. The plate is just a wide bar. The vise is a vise but includes some sort of angle locking mechanism and the two cylinders to allow precise angle setting. Like a lot of precision tools, spend as much money as you want for increasing precision well in excess of the average hobbyist’s needs.

Madly Off in All Directions

Some may be wondering about the recent focus on machining related topics. The pure model railroading has been on a bit of a hiatus as I get geared up for some model engineering. The latest project, and it is indeed a project, is a new milling machine! I am not changing direction just adding more of them or at least the distances I can travel.

Why Get One?

After my initial experimentation with milling on the lathe, I concluded that I needed more capability to accomplish my long term goals. Getting set up was an involved process and once there, the milling “envelope” was small and speeds available were limiting. An end mill smaller than 3/8″ would require spindle speeds in excess of the Myfords ~1000 RPM top speed.

Why This One?

My model engineering aspirations date back more than 40 years so it definitely not an impulse buy! I essentially compromised on the biggest bench mill I could imagine safely fitting down the basement stairs and onto a stand in beneath my 7 foot ceiling. I suppose if I eventually end up with a ground floor shop I might add a full sized Bridgeport type mill but this ought to do and I am proceeding on that assumption.

Based on the assumption that the mill acquired would it for the rest of my life, I set out to find as good a mill of not more than about 400lbs with as many bells and whistles on it as I could manage. And that I could bring myself to pay for.

The pay for part meant either a used mill of North American or European origins or a new one of Asian manufacture. While I wouldn’t say no to a Schaublin, Deckel or Fehlmann, the new ones are way more than I could justify. A multiyear search for used bench mills turned up effectively no candidates. Lots of big manual knee mills but not bench mills. They are out there in Canada because I have seen Tom Senior mills in other people shops but nobody was selling one where I was looking. It looked like buying new was the way forward.

After considerable research, I landed on the Precision Matthews PM-728V-T. It is made in Taiwan to claimed higher standards than most modern imports. Here are the features that I considered important:

  • square column: two axis to tram is enough
  • pre-installed 3-axis digital readout(DRO): counting turns of the handwheels and allowing for backlash got old quick on the Myford
  • power x-axis feed: x is the side-to-side direction and the usual one involving a lot of cranking, at .100 per crank, 20 inches is a long way
  • 370lbs: I could imagine managing that
  • R8 spindle: this is what Bridgeport’s have and tooling is abundantly and locally available.
  • 120VAC power: three phase is not somewhere I want to go.

Current Status

Getting the thing out of the driveway, down the stairs and on to the stand was an incremental production of about 5 days, mostly spent in preparation: building a ramp, a gantry, removing doors and handrails, etc. (Moving 400lb lumps of iron is not the time to be lackadaisical)

After the mill was in place, various infrastructure and assembly tasks were needed before any actual work could start. Assorted tooling was required as well which was a challenge in the current lockdown in Ontario.

All that being said, chips are being made and I expect everything to settle back into balance with layout construction in the near future.

Bandsaw

Part of my recent experimentation with milling on the lathe involved cutting some steel bar stock roughly to length with a hacksaw. 1/8 x 3/4 bar wasn’t too strenuous but 1 1/2 x 3/4 was way too much like exercise. After considering the alternatives to just quitting, I settled on as cheap a horizontal/vertical bandsaw as can be got the imported 4×6, in my case, the Craftex CX122. Back-ordered during the “Black Friday” echo sales we get in Canada due to proximity to the US, I picked it up on the afternoon of New Year’s Eve.

Assembly was a bit of a challenge due to less than stellar documentation but I think I have it together correctly. I say think because the instructions included a list of required tools and a reference to a loose parts list but neither actual assembly instructions nor the aforementioned loose parts list. </rant>

Anyway, after a fair bit of squinting at the tiny exploded parts diagram and replacement parts list (all the parts of the entire machine, not just those to be assembled) I had a saw and no leftover parts. This, of course, required something to be sawn.

I chose a round bar of mystery steel offcut the metal vendor threw in with my first order because it was bent over part of its’ length. (I don’t want to be there when 1 inch steel bar gets accidentally bent!) Cutting off the bent bit is a useful thing and low commitment if things went pear shaped. I set it up and fired up the saw. After a good while, I had two pieces of steel and no catastrophe. I did realize belatedly that the drive belt was insufficiently tensioned and did correct that. That bit was in the instructions so was entirely my fault.

The cut is nice and smooth and reasonably straight and best of all, my arms do not feel as if they are going to catch fire or fall off. Metal working is looking more enticing already.

Roller Gauges: Design Meets Reality

Two Proto:48 Roller Gauges

When I got to actually laying out the dimensions on the first gauge (ie, marks in big Sharpie with dial calipers, I belatedly realized that the .036 flange width on the ends would be very delicate and vulnerable to damage if one, er, hypothetically dropped one on a concrete floor. Which is why my previous efforts had .100 rims rather than aspire to fit right in the frog of turnouts. I opted to repeat that choice for durability’s sake.

Being an aspiring novice hobby machinist, there are things I know need improving in the execution of these parts. Measuring those small gaps with dial calipers isn’t the most precise method but all I have that works. The finish isn’t as smooth as it should be which I know how to fix but will require developing my tool bit sharpening skills. There are probably things I don’t know that should be improved, too.

Anyway, parts done and sent off into the pre-Christmas postal maelstrom.

Milling About

I haven’t been doing much directly on Comstock Road recently but I have not been entirely idle. Having acquired the lathe and producing some roller gauges, I had not done much with it since. I recently resolved to get a better grip on the lathe’s capabilities and improve my rudimentary machining skills.

The lathe came with a vertical milling slide that bolts to the cross-slide and can be a substitute for an actual mill, up to a point. Being sparsely supplied with t-nuts for attaching things to either slide, I set out to mill down some that came as part of a machinist’s clamping set. (The Myford t-slots are 3/8″ wide but the cross of the T is both thinner and narrower than standard and the vertical part of the T is shorter.

Here is what the milling slide setup looks like:

Getting to that point definitely involved some learning opportunities:

  • I figured out how to read the change gear chart and reduced the feed rate which involved removing and reinstalling some things where washers at the wrong place caused gears to interfere with covers.
  • Got the spindle drip oilers adjusted, more or less. Cleaned grease out of various oil fittings and hopefully got things properly oiled.
  • Filed down a t-bolt to get it to fit so I would have enough to secure both milling slide and vise.
  • Ground the vise mounting lugs out with a rotary tool to get said bolts to fit.
  • Figured out how to square up the slide and the vise.
  • Worked out how to use a dial indicator to measure travel on the carriage.
  • Learned to not bump said indicator in the middle of an operation…
  • Learned that locking the carriage before doing a milling pass was not optional!
  • Much learning about work holding.

I had two exciting failures in workholding resulting in a missing chunk from the top corner of a nut in one case and, in the other case, jamming the whole spindle. Neither was catastrophic.

Here is one of the resulting slimmed down nuts, ready to hold something down. The first something is likely to be a carriage stop since using a dial indicator to measure carriage travel is a bit insecure. I intend to eventually work my way up to some sort of small live steam engine.