Member postings for Andrew Johnston

When I made the worm wheel for my traction engine governor I used a 7/16" UNC spiral flute tap, quite coarse for the size at 14tpi:

Tap was bought secondhand on Ebay for a few pounds.

Andrew

Simple, for any given diameter choose the smallest TPI, or largest pitch. Realistically any single start thread is unlikely to have a helix angle of more than a few degrees. If a higher helix angle is needed then it would be better to make a cutter and cut the knurls by indexing. Free hobbing with a tap is hit and miss at the best of times.

Andrew

Almost certainly not; the resolution may be 5um but the accuracy will be less, possibly far less. My Newall microsyn scales are 5um resolution, but 10um accuracy. Each scale comes with a card showing measured accuracy versus length.

Andrew

First analyse the part and work out a geometric design sequence in one's head. We can see that the part has symmetry around mid-depth (ends are mirror images) and also has rotational symmetry around the vertical axis. First sketch creates the outer rim and cylinder, and the inner cylinder, which are then revolved around the Y axis:

I'm using the XZ plane for mirroring. If I was going to 3D print or CNC mill the part i would have taken care to orient the part with respect to the XY plane, as that makes it simpler when importing the part into a slicer or CAM program. Only half of the part is modelled. There's no point in drawing, and dimensioning, both ends. Although not obvious in the above picture the inner cylinder is lower than the outer as per the original part. Add a spoke using the top of the inner cylinder as a reference plane and extrude to the XZ plane. The spoke is constrained to be symmetric about the X-axis and the width is dimensioned. The length of the spoke is unimportant (not dimensioned) as long as it overlaps the inner and outer cylinders:

Use the circular pattern function on the spoke extrusion to create the remaining spokes:

Add fillets:

Mirror everything about the XZ plane:

Andrew

A slap in the face with a wet fish is in order.

The original post asks how a preferred CAD package would create the given part. The latest post then says don't "cheat" by using revolve. The object is round so revolve is a logical operation; how is that cheating? I'd use two operations to create the "simple" shape; revolve followed by mirror.

Andrew

Exactly; created this in five minutes in Alibre:

I suspect my method is a bit involved, as it includes extrusions, revolutions, circular patterns and a mirror operation.

Andrew

Actually 0.4mm; in another thread weren't the proponents of the metric system saying it avoided hiccups due to the simple multiplication factors?

Andrew

I suspect you really need to be using a hefty machine vice rather than a toolmakers vice.

Andrew

I was thinking more of equating 30mm with 1 foot, an order of magnitude out.

For the example given I happen to know that 19.05mm is exactly 0.75", so just subtract 2 thou. Depending upon what I am doing I tend to work in imperial or metric, so rarely need to convert, at least to any degree of accuracy. If I do, it is done beforehand in the planning stage and written on the drawing.

Andrew

Could be that people are unable to do basic arithmetic?

Andrew

Chip loads seem low, I normally run face mills at 0.1mm chip load and upwards. The inserts need to cut, and that is achieved by a combination of depth of cut and chip load.

Andrew

Low carbon steel will be fine. Casehardening would be icing on the cake, but isn't strictly necessary. When I made a drawbar for my horizontal mill I used EN16T, but only because I had the needed 16mm diameter in stock.

Andrew

I expected that nylon would be significantly more expensive, but thought I'd let you decide.

I make my formers out of hot rolled steel, but I normally form red hot, like the flanges on this spectacle plate from 3mm sheet:

Andrew

Any commercial stockholder should stock thicker sheets, such as EDPlastics:

EDPlastics

Nylon plate up to 100mm thick.

However, plastic is the wrong material. Wood or metal would be a better choice, especially for stainless steel.

Andrew

I'd agree with Robert, waaaay too much spindle extension on the tool. Plus the work isn't really clamped tightly enough for running a face mill. Lastly 2 thou depth of cut is not really making the inserts work properly. Combining any two of the three is probably enough to induce chatter. This is the ideal for face milling, rigid tooling and everything clamped down:

Andrew

The holder that uses inserts at 45 degrees can only machine surfaces that are open on all sides. The holder that uses inserts at 90 degrees can, in theory, machine a surface that has a shoulder on one, or more sides.

Andrew

Although PathPilot (used with my Tormach) has a wide range of wizards, I've never used them. At some point I'll try the thread milling ones, out of interest.

I'm not sure why mathematical profiles are a problem? My CAD system will import spreadsheet numbers to as much resolution as one wants. I use it for involute profiles. I always design my gears as 1DP and then scale down as the last operation before exporting to CAM. So errors can be made arbitrarily small.

Andrew

I use a 6" machine vice on all my milling machines, including the Bridgeport. It's a Kurt D688, opening is 8.8" to 17" depending upon jaw position. Possibly a little large but it was cheaper than the alternative, slightly smaller, Kurt vice. I have the capability to take heavy cuts on the horizontal mill so need a solid vice to match.

Andrew

I've just signed up with Hobbyweld for 9 litre oxygen and 10 litre acetylene. Of course one has to pay a deposit, but gas prices are on a par with my previous rental agreement with Air Liquide. My local Hobbyweld agent charges a very reasonable £6 for delivery, as opposed to the £60 Air Liquide wanted. When I signed the agreement and collected the first set of bottles the agent agreed with my reading of the regulations, ie, for small bottles, and as a private user, it is perfectly legal for me to transport the bottles in my car, provided I ventilate the cabin. In other words open the window.

Andrew

I wait for a fairly calm day, say less than 10mph. I tried silver soldering in an empty greenhouse to shelter from the wind, but it wasn't successful.

Andrew