Author Topic: First build from castings  (Read 2055 times)

Offline Allen Smithee

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First build from castings
« on: March 28, 2020, 10:25:40 PM »
To date I've kinda stayed away from castings - I guess it's the lack of flat datum surfaces that put me off. But a few years ago I came by one of the Bruce Engineering external hone kits and over the last couple of days I decided that I had to overcome this aversion. So here it is:




Of course the castings are only aluminium, which makes it easier. But they were slightly warped (twisted) which meant having to be careful to choose the positions for the through-holes so that the didn't get too close to edges on the other side. Needless to say I found it far less fraught than I had feared - having chosen a datum face and machined it flat the rest was just a matter of looking at the drawings, thinking about how to hold the job.

In fact of all the daft things - the only bits I had trouble with were the two 1/4" pins. These each have cross-drillings in the middle - one to be tapped 4BA and the other a 4BA clearance. I'm embarrassed to admit that I had four goes at making these before I got usable parts! I ended up clamping a long piece of 1/4" stainless between two V-blocks and then carefully establishing true centre (using an edge finder) to centre-drill and then drill/tap without moving any axis other than the quill. The pins were then cut out of the bar and faced to the required lengths.

Anyway, that particular dragon is now slain!

AS
Quidquid latine dictum sit altum sonatur

Offline crueby

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Re: First build from castings
« Reply #1 on: March 28, 2020, 10:32:32 PM »
Nicely done! Do you know what it will be used for first? honing valve rods, pistons?


For drilling centered holes crosswise in round rod, a trick I was taught was to take a piece of flat or square stock thicker than the rod, clamp it in the mill vise (with the vise lined up to one of the axis on the mill) and drill a hole in it the size of the rod. Hole does not have to be centered - just so the hole doesnt break through the side. Keeping the mill table locked down, turn the fixture 90 degrees so the hole is sticking out the side. Then insert the rod in the hole, and drill your final hole through the fixture and rod. Since the table was kept locked, the center of both holes are in line with each other. I used this to drill a hole batch of rods for cotter pin holes, worked great.

Offline Don1966

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Re: First build from castings
« Reply #2 on: March 28, 2020, 11:15:27 PM »
Nice work Allen love the hone!



 :cheers:
Don

Offline Allen Smithee

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Re: First build from castings
« Reply #3 on: March 28, 2020, 11:35:53 PM »
Well they said that for the duration of the crisis I needed to be at hone... ;D

I tried that drilling-through-stock trick, but the drill wandered when it got to the pin. Really odd, because it wasn't especially hard material or anything.

AS
Quidquid latine dictum sit altum sonatur

Offline crueby

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Re: First build from castings
« Reply #4 on: March 28, 2020, 11:44:43 PM »
Try it with the block and rod the same material. Or maybe with the block harder than the rod? Hmmm...

Offline awake

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Re: First build from castings
« Reply #5 on: March 29, 2020, 12:19:49 AM »
Nice ... and extra points for the "stay at hone" pun! :)
Andy

Offline Allen Smithee

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Re: First build from castings
« Reply #6 on: March 29, 2020, 12:27:24 AM »
In the end it was achieved with just taking care to position very accurately and then using a centre-drill small enough that it thought the 1/4"dia rod was a flat surface. I then ran it at about 100rpm until the centre was established in the hole, slowly ramping up the speed. Then I did the same with the drills - start very slowly with lube, and ramp up to 1200rpm or so once the hole position was established.

Every day is a school day...

AS
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Offline Jo

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Re: First build from castings
« Reply #7 on: March 29, 2020, 08:19:40 AM »
 8) That looks good Pete,

Now that you are on a roll what are you planning on making in the next 11 weeks of holiday lockdown  :)

Every day is a school day...

For those of us who are retired every day is a holiday, think of this as a bit of pre-retirement practise ;)

Jo
Enjoyment is more important than achievement.

Offline Allen Smithee

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Re: First build from castings
« Reply #8 on: March 29, 2020, 08:41:38 AM »
8) That looks good Pete,

Now that you are on a roll what are you planning on making in the next 11 weeks of holiday lockdown  :)

Sadly I have quite a bit of actual work to do during the week. But I have the VDH to finish off, and to drill the plates I'll need to finish and install the headstock divider. Alongside those I have that 10cc 4-stroke diesel to finish, and then a couple of CM1.4 diesels to make, and I nearly have all the materials I need to make the coffee-cup stirling engine.

That should keep me busy for a couple of weekends.

AS
Quidquid latine dictum sit altum sonatur

Offline Allen Smithee

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Re: First build from castings
« Reply #9 on: March 29, 2020, 02:59:58 PM »
When I bought my Myford the nice old biddy I bought it from threw-in a part-built headstock divider (the GHT one). I put it to one side because it needs the plate/finger assembly from a VDH which I didn't have at the time.

Fast forward a few years and I managed to come by a part-built VDH for a silly price (a few years after that I found a tailstock and milling risers kit second hand, so I have now everything!), so it's been on my to-do list to complete both dividers for a while. George Thomas's process for making the VDH uses the headstock divider to make the division plates so finishing the headstock divider comes first.

Step 1 - mount it in the lathe (drilling at tapping 3 holes!):



The shaft bush has been removed and put on the front for reasons that will become clear in a minute.

Step 2 - dig out my VDH parts and extract the shared components:



The main shared parts are the wormwheel and the associated clamping collars, finger plates etc (also the microdivider, but that comes later), and this is where I came to a small snag. As these two units were made by different people (or perhaps just due to some minor surface corrosion) there are minor differences in sizing. Specifically - the bore in the wormwheel is a couple of thou smaller than this shaft bush:



I don't want to touch the wheel because it fits the VDH, so now we come to why I'm posting this blather in this thread.

Quote from: Crueby
Do you know what it will be used for first? honing valve rods, pistons?

Neither. I think its first job will be to gently take a thou or two off this shaft bush.

And so the story comes full circle. My work here is done - I must go to other threads than need me...

 8)

AS
Quidquid latine dictum sit altum sonatur

Offline Allen Smithee

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Re: First build from castings
« Reply #10 on: March 29, 2020, 05:05:26 PM »
Addendum - it did indeed do the job very well and much more quickly than I expected. In two 15-20 second bursts (using cutting oil and running at 700 rpm) cut a measured 0.035mm off the dia at which point the wormwheel slid smoothly on with no detectable play (far less than the couple of thou I had estimated. The shaft diameter varies by about 0.015mm over the length but I forgot to check it before I started so I don't know if the hone did that or not. Anyway, it seems to work nicely and is easy to use.

My work on the dividing heads has again shuddered to a halt because both of the previous builders fottowed the damn drawings slavishly, so the shaft retaining the disks has GHT's recommended 1/4BSF thread rather than something more rational and more this century (like M6!). I could have sworn I had a set of 1/4BSF taps and die, but I can't for the life of me find them so I will now have to find one of the small "run from home" suppliers who (a) has them and (b) is still trading by post!

But that's for a different thread [sic]

PDR
Quidquid latine dictum sit altum sonatur

Offline Admiral_dk

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Re: First build from castings
« Reply #11 on: March 29, 2020, 09:27:23 PM »
Quote
Alongside those I have that 10cc 4-stroke diesel to finish, and then a couple of CM1.4 diesels to make

Any chances of pictures of those when you get so far please ?

Per

Offline Allen Smithee

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Re: First build from castings
« Reply #12 on: March 29, 2020, 11:30:24 PM »
Of course.

Meanwhile, I found that Modelfixings carry toolsteel BSF taps and dies, and they are continuing to operate as a web-business, so I should be able to continue in a day or two.

PDR
Quidquid latine dictum sit altum sonatur

 

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