Not a model engine!

[Allen Smithee]

PLEASE NOTE: This thread isn't about a model engine - it's about doing a favour for a friend and gaining machining experience. My primary reason for posting it here is to get comments on how I've approached the task, the setups I've used, and suggestions for alternatives so that I can learn from the expertise and experience of others!

So a friend of mine has a ageing boat whose decaying fittings can be troublesome to replace. One of those fittings (well three of them, to be truthful) is the catch system for windows in the lower hull. These are based on some mazak die-castings held to window frames with countersunk pop-rivets. The original (damaged) item looks like this:

AS

[Allen Smithee]

As you will quickly see, the only flat/straight datum surfaces are the two outer faces (just to add some challenge). In my material pile I had some 20mm square aluminium bar, and a quick check suggested that the whole bracket would fit entirely inside a 20mm cube so I sawed off three pieces of the bar and trued them up to make said 20mm cubes. After that (I reasoned) it would just be a simple matter of carving away all the aluminium which was not part of the bracket...

AS

[Allen Smithee]

Looking at the shapes I decided the first task would be to mill the 10.5mm wide, 12.5mm deep channel through the middle. I clamped the three cubes side-by-side so I could do this in a single setup. My mill is a tweaked Seig X2p, so this had to be approached carefully to avoid chatter, but with a 9.5mm slot drill it gamely chomped its way through in two 5mm cuts, following up with a 10mm four flute cutter to finish the width in two 10mm-deep cuts and then a finish run along each side to get a clean cut of the bottom. This worked well, but there was a tendency for the swarf to re-weld to the cut faces - does this mean I'm running the cutter too fast? When milling I tend to run the Seig flat out (2,500rpm) unless there's a specific reason not to, so perhaps I'm pushing it too hard here?

AS

[mike mott]

I'm surprised they were not bronze or stainless.

Mike

[Allen Smithee]

I removed and deburred the parts, and decided that this would be a good time to drill the various holes (the countersunk one for the mounting rivet and the cross hole for the pin) as at this point I had datums I could work from. The brackets were clamped in the mill on parallels, using the holes spotted & drilled. Finally the countersinks were cut in the top surface.

Not happy with the countersinks - no matter how carefully I do this, and with decent tools, I can never seem to drill countersinks without chattering. Is there a knack to this?

AS

[Allen Smithee]

Next I decided to cut the mounting face - this had a flat side and a bevelled side (presumably to match the profile of the window frame). I wasn't sure how to approach this, but I was "inspired" by the "milling by eye" approach Tug uses to emulate castings. So I marked the required angles with a scriber and carefully positioned the job in the vice, lining up the scribed lines parallel to the jaws of the vice by eye. I then cut the bevelled surface in a series of careful cuts by eye. I then repositioned the part flat against parallels to cut the flat face. Obviously I had to repeat this for the other two, and each had to be separately marked, positioned and milled.

I was quite pleased with the result - lining the parts up with the original shows the angles are all near enough for government work!

Mind you, this was one of those occasions when some angled-parallels would have come in handy so I guess they go on the wish-list...

AS

[Allen Smithee]

The cross-holes were finished off by drilling one side to 6mm so that an M5 tap could be run through this hole (to align it) into the other side (didn't bother photographing this). The final step for these brackets was to cut away some of the material to bring them closer to the cosmetic profile of the original. Again, this was done "by eye" and again it had to be done separately for each part.  If I get time (and can be bothered) I'll make some filing buttons so I can put the radiused profile on the top, but that can wait.

AS

[Allen Smithee]

Attention now moved to the cross pins. In the original these had just been a 3mm mild steel screw, and it had become severely bent by the tightening loads - it had to be sawn and drilled out of the original so I could measure-up the casting.

I decided to make the new pins rather larger and stronger. I had some 8mm "finest gash DIY store" stainless bar so my design would have a 5mm main shaft tapped M5 at one end, a 6mm head with a sawn screwdriver slot. None of this is rocket surgery so I decided not to take picture of the turning operations. The results worked quite well, although the "gash stainless" had an amusing habit of work hardening and then glowing bright orange sometimes while being faced and parted (but the cheap insert tools I used didn't seem to care). The results are shown below, together with the one that decided to harden along its whole length while being brought down to 5mm. It's a lovely colour, and is now hard enough to survive local thermonuclear shocks...

AS

[Allen Smithee]

The final item was the main shaft. After the fun with the gash stainless I decided not to try to use it for these. As it happened I had some M8 stainless bolts (screwfix?). The threaded portion was exactly the right length (so close that I'm even wondering if the originals were manufactured from bolts rather than bar stock), so it was just a matter of parting to length, tidying up the ends and then cross drilling in a V-Block. These bolts machined beautifully, btw. Shown below together with the bolt they came from (only two are new - one is the original part that I've just drilled out to 5mm - there will be a brief round of applause for the first person to identify the original and point out what is different about it).

AS

[Allen Smithee]

Finally an assembly shot to show they do all fit together. The one with the original shaft is fitted with the knob unit used in the boat. I still have to work out how to make two more of those. In fact if anyone has suggestions please jump in - the functional features are the metal flange at the base of the knob and the hand grip on the knob itself. The original is something like bakelite moulded over a stainless core but that's beyond my facilities. I have some 40mm stainless bar, but machining the whole knob from solid sounds like serious overkill (and would probably be too heavy).

Any ideas?

AS

[Jo]

Well done Pete,

Jo

P.S. Could we have slightly larger photos say 600 by 800 pixels? 

[Allen Smithee]

Sorry about that! I did a bulk-resizing of the pictures and I think overdid it - I'll see what size comes out at about a meg per pic and go back & replace them. Mind you, they're only phone shots so they mayt not be that great even then...

AS

[Allen Smithee]

I turns out the problem was that the app I was using defaulted to png format. Switching that back to jpegs made the files much smaller.

I'll swap them out now.

I've now swapped all the photos for bigger ones.

AS

[crueby]

I needed knobs like that for my car roof racks, the originals were cracking from being in the sun so many years. Found ones online, plastic knobs with steel threaded inserts. Much easier than making them. The woodworking catalogs have them for making fixtures and clamping rigs.

[Allen Smithee]

The knob is a slightly more complex problem than it might seem. In use the metal flange at the base of the knobhooks in front of a u-shaped yoke (attached to the external frame) to push the window shut against its seals. So this flange sees a constant load trying to pull it off the rest of the knob. I'm going to have to make this base flange as a separate part, probably in stainless. I could turn a press-fit boss on the metal insert in the handle and then press/loctite the flange in place, but I feel that over time (especially with winter-summer temperature cycling) the press/glue joint may relax and fail. Having the window move back from its seals when berthed would be inconvenient, letting the rain in. But having it happen when under way could be a safety-critical hull breach, which the boat's owner considers a Bad Thing^(TM) (damned sunny-day wimp sailors!).

Ideally I want to have the M8 thread of the stud in the flange itself, so that the knob/flange joint is just taking the torque loads of tightening/loosening the catch. So I'm looking for a knob that I can adapt for that sort of thing. I'm currently working my way through this catalogue which is looking promising...

AS

[Steamer5]

Hi Allan,
 Just catching up.
Made some knobs along those lines for my bandsaw upgrade.

I turned up the large part from aluminum, the threaded bit I turned up from steel & glued it in. The finger grooves were cut on the mill, you need to hold the part tight, don’t ask how I found that out, you need to spend a bit of time taking the sharp edges off the grooves. Hope that make sense. In your case the flanged bit at the bottom would be part of the steel insert.

Cheers Kerrin

[Allen Smithee]

The stuff arrived, so here's how I finished the job. The remaining part comprises the plastic knob (22p each from a UK supplier) and a part turned from stainless:

AS

[Allen Smithee]

As this would need a lot of metal removed I decided rather than risk poor machining from "gash" stainless I bought some pukka 1" 303 bar from M-Machine. This machined beautifully with a cheapish carbide insert tool, and the central bore drilled easily with a standard HSS drill bit.

I decided to do all bar the final tapping without removing the the bar from the chuck, just parting off and then reversing in the chuck to face to length before tapping the bore. This plan worked well, except for the usual hazard of turning a reverse taper - I swung the topslide to get the 13.5deg taper and it worked well EXCEPT that on one cut I forgot that you have to back the tool fully clear of the largest diameter before winding the saddle back for the next cut 

Fortunately the tip survived and the gashed-up surface was all in the waste metal that was cut away later.

My lathe (Myford S7b) is not brilliant for measuring along the bed axis - the leadscrew handwheel has a micrometer dial, but both the handle and the dial are tucked under the right-hand end of the bed and are a pain to use. I have a DRO which I keep meaning to fit to the saddle but haven't gotten around to yet. So mostly I set up a saddle stop and use the topslide for accurate dimensions, but of course I couldn't do this with it set up for the taper. So my cunning plan here was to mount the material in the chuck and then cut a shallow parting groove to use as a datum - all axial dimensions were measured from here using a vernier and steel rule. Crude though it was the method worked well enough, but I must get that DRO mounted!

AS

[Allen Smithee]

Finally the plastic knob was simply drilled 10mm and then opened up to 11.8mm with a boring bar. The resulting firm press fit was extremely satisfying and seems more than adequate. I'm quite pleased with the result. The final picture is one of the existing ones that's still in the boat, to show how it's supposed to work.

Now I just have to make a couple more and work out how much to charge him...

AS

[Jo]

Now I just have to make a couple more and work out how much to charge him...

I would just keep the spare stainless as payment and give him the bills for all the materials used  .

Jo

[Allen Smithee]

Job finally finished. The attacked show the stainless machined part and the finished latches (one with the original knob and LH thread). I've learned a lot in the process. I'm quite pleased with the way my little myford handles biggish chunks of 303 stainless, and I'm learning more about which types/shapes of tips cut better at what kind of cut. I still found that all the insert tools were better than the toolsteel ones, which isn't what others tell me, but I guess that's telling me I need to learn how to grind them. I also now see the benefit of buying pukka materials rather than some "might be" materials from cheaper sources...

AS

[Ian S C]

I'm no good when someone asks"How Much", so I tend toward asking the customer for their idea of a price, and more often than not it is above what I had thought of.
Ian S C

[Vixen]

Now I just have to make a couple more and work out how much to charge him...

The price you ask should reflect how much you want them to return with more work for you. Better way than offending them by saying NO

[Allen Smithee]

Now I just have to make a couple more and work out how much to charge him...

The price you ask should reflect how much you want them to return with more work for you. Better way than offending them by saying NO

I'm not looking for more work - this was just a favour for a mate. I told him that the bought-out costs (knobs and materials) came to around £30, and invited him to bung in whatever he thought appropriate for my couple of afternoons. He came straight back with an amount I'm quite happy with. For me the time spent was just further useful familiarisation with my machines, learning how to get better results from them. I wasn't really looking to make money on it - if I was then I'd have to charge the £110/hr rate that my company bills projects for my time and that would have made the whole project non-viable.

AS