Member postings for Andrew Johnston

I was looking at the Cutwel site. Oddly the Korloy specific inserts don't include a radius, but the ISO inserts do include a two digit radius size, after the insert code.

Andrew

Jason/Ron: Thanks for the information and practical results.

I'm not worried about variations in thickness, but inconsistencies in length/width do worry me. It's good to know that the inserts fit anyway. Looking at professional tool suppliers the insert side angle seems to be 11°, although I don't think that's set in stone.

I looked up the coding for inserts. The PDER and PDFR decode as follows, basically in accordance with what has been previously posted::

P - cutting edges are at 90°

D - Wiper relief angle is 15°

E/F - Cutting edge condition, E is rounded, F is sharp

R - Cutting direction, right

Man, this stuff is complicated. I'm concerned because I got done on the 80mm face mill I've previously alluded to. It was very expensive but the range is now obsolete, as are the inserts. I've been buying up inserts on Ebay. I've got about 50 now, and with 4 edges per insert that should see me out.

The Arc part number misses out the corner radius, although that's not an issue as they only supply one value.

Andrew

Beaten to it again - must learn to type quicker!

Edited By Andrew Johnston on 02/01/2020 16:15:10

When I made a punch and die used to punch out an odd shape in brass (so a connector could be snapped in into place) I used silver steel and gauge plate. I left them unhardened. I wouldn't waste my time trying to adapt unsuitable tooling. Just use silver steel for round punches and gauge plate for everything else. For thin material probably not worth hardening, but for material above 10 thou or so I'd harden both punch and die. Silver steel and gauge plate are not quite the same. Silver steel is intended for water/brine quenching while gauge plate has extra alloying elements and is designed for oil hardening. Although of course water is fine for non-critical appllications.

The punch needs to be slightly smaller than the die. The thicker the material to be punched the smaller the die needs to be.

Andrew

Don't use multiple software packages written by computer geeks?

Mind you even using semi-professional 3D CAD I had problems modelling the smokebox nameplate for my traction engines. Although most of the issues revolved around having to use a non-linear scaling on the characters as none of the standard fonts had the correct height/width ratio. And then having to convert an assembly to a 'part' so I could create the CNC tool path.

Andrew

Since my internal gear and pinion were designed as 1DP it's simple to scale to 40DP. Here are the results:

By no means perfect, but this was using a 0.4mm nozzle. Just scale, export, inport into the slicer and use the standard settings. Plastic is PLA.

Andrew

Ketan: Thanks for the notes on inserts. The more I look at it the more I'm put off buying. I've been looking at inserts from Cutwel made by Korloy. They seem to measure insert length in a slightly different way so it's hard to compare like with like. Even in the Arc calalogue the length and width of the two inserts on offer are different. How does that work in the machined pocket?

Cutwel do inserts that almost exactly match the Arc part numbers, but are specifically for the Korloy Alpha Mill series. They also do ISO standard inserts. In this section the inserts are stated to be generic but the part numbers differ from Arc in the detail. Specifically what is the significance of the PDFR and PDER parts after the style and size code?

I apologise for being a pain but as always in engineering the devil is in the detail and I don't want to waste my money!

Andrew

This is a magnified view of my 10DP internal gear and pinion:

The involute curves are a fair representation and the gears mesh smoothly, and just as well as the final metal gears.

Andrew

For my traction engine gears I downloaded some DOS applications that create a gear in DXF form, which was then imported into my CAD program. I used the hi-res versions which use about 20 points. The original DXF, and gears, were drawn as 1DP and then scaled down to the final size. That way any errors are reduced.

For the internal gears shown I used the equations for the involute of a circle (*) to generate points in spreadsheet which were then imported into CAD. Can't remember how many points, but probably 10+. Again the gears were designed as 1DP and then scaled to 10DP for the 3D printed gears. Next year (!) I'll take some close ups of the gear teeth.

One thing that puzzled me when starting to design gears was what is the diameter of the circle from which the involute is created? Turns out it's called the base circle and is the PCD times the cosine of the pressure angle. For small numbers of teeth the base circle can be larger than the root diameter, ie, no involute curve near the root. In practise this isn't too important as the root diameter is smaller than theoretically needed to give clearance. For the internal gear i approximated the curve between base circle and "root" diameter by a straight line.

The old (50+ years) metal Mecano gears I have are a bad approximation to involute teeth.

Andrew

* MG is correct, an involute is simply a curved derived from another curve; the involute used in gear design is specifically the involute of a circle.

Equally it was a throw away reply.

I don't think it's a simple as saying the resolution can't be better than the nozzle size. Certainly one can't print a feature that is smaller than the nozzle size. But if the feature is larger then the accuracy is determined by the accuracy of the moment rather than nozzle size. It also depends upon whether the slicing software takes into account the nozzle size when creating the outline of the part. That's much the same as a CNC mill offseting the cutter path to account for cutter diameter when profiling. My feeling is that Cura does take into account the nozzle size. The internal gear set meshed very well and smoothly. If nozzle width wasn't accounted for the gear set could be out by 0.4mm. I'd be disappointed if I hadn't noticed that. Since I didn't I assume it wasn't there.

Andrew

Ketan: Thanks for the update on the shell mill arbors. I'll wait until the new arbors are in stock. The inserts are supposed to be generic. Does this mean I can buy them from elsewhere (an industrial supplier) and they'll fit?

I plan to buy a 40, or 50mm, body for use on the Bridgeport and a 63mm body for use on the horizontal mill. I've already got an 80mm indexible shell mill for the horizontal. The mill has a 5hp motor so I hope to give the cutter a run for it's money in terms of DOC, WOC and chip load. The only limitation is that maximum spindle speed on the horizontal is 1200rpm.

Andrew

There is a rule of thumb that says a width of cut of about half the cutter diameter is bad; it shock loads the teeth/inserts. Better to use less than a third, or more than two thirds.

Andrew

Paul: Thanks for the additional information. I'm hoping to avoid packing, but if needs must!

This morning I've finished a batch of ~70 1/4" BSF nuts. For each nut chamfer the underside to remove the parting off burr and then tap. Took about 15 seconds per nut. Next job, in the New Year, will be to finish off the heads on the corresponding bolts but that will needl a change of collet.

Andrew

I suspect the Shannon-Hartley theorum of channel capacity would be more useful. Given the low data rate we either have a narrow bandwidth channel or a low S/N ratio.

SoD: That looks a rather weird gear tooth shape? It almost looks like two straight lines joined by an arc. I'd expect the involute function to be a smooth curve. Once I've sobered up in the New Year (!) I'll have a go at printing some more (smaller) gears and also thin wall features.

Andrew

Paul: Thanks for the pictures; that's a neat looking job. It'll be a fallback for me if I fail to flange properly. I'm going to have at least one more go at flanging. The existing plate isn't bad, but in retrospect I didn't get all of the flanges close to the former. That's partly my own fault for finishing late at night when it was dark, and I was running out of gas. On reflection I feel that I'm pretty near to getting flanging to work to an acceptable standard. The fullsize engines aren't perfect; so as long as I match them I'll be happy. I've also learnt that I can cut down on my allowance for the flanging which should make life easier. Especially on the corners where the excess metal causes the flange depth to grow. I've designed for a 3/4" flange and allowed 1", the excess being machined off. I can cut the allowance down to 7/8" and for the corners I can go down to 3/4" or even slightly less. Roll on the New Year when I can get some more gas!

In the meantime I'm knocking out the 1/4" BSF bolts and another batch of nuts on the Britan that I'll need to fix the plates.

Andrew

No idea about tooth strength, but I'd be more worried about wear. If you can draw the gear then you can 3D print it:

To get solid teeth I just increased the wall thickness to make the teeth solid, while leaving the body with infill. The gear tooth shapes as shown were accurate enough to exhibit trimming interference. Changing the pressure angle solved the interference issue.

Andrew

Use a coarse tooth saw and I'd do the cut in two passes from the side. Rather less encouraging is that the only way I've found to stop a saw going walkies on a deep cut is to use the horizontal mill, as it is much more rigid and the arbor provides better support for the saw than the Bridgeport.

Andrew

Yebbut they're not what I wanted!

Andrew

I just tried ordering some indexible bodies and arbors from Arc. Both R8 and ISO40 arbors are out of stock, with no restock date. Seems pointless to review items that one can't buy.

Andrew

The spectacle plate now fits:

But I'm not happy. It doesn't match the picture in my mind of how it should look, so it isn't acceptable. It feels a bit like a school report - in my case they normally said "could do better" or "could work harder". I haven't given up on flanging yet, but ultimately I'll weld a flange onto a plate rather than trying to form it hot.

Andrew

PM sent to the OP.

Andrew