Len Mason's "Mastiff" - chewed from the solid

[deltatango]

On to the last few Mastiff bits for 2017...

The camshaft cover has the oil filler hole and four screw holes but is otherwise very plain. The blank plate was milled to thickness leaving the filler hole boss square. Lots of chips for those who like chips:



and the boss turned circular in the 4-jaw:



I drilled and tapped the last few holes in the crankcase and blocks, drilled the fixing holes in the camshaft cover and screwed everything together to make a lump of bits that is starting to look like an engine:





It all turns over and the valve timing looks OK to a first approximation.

I've started work on the conrods but we are moving to the coast for Christmas in a couple of days and the workshop gets left behind until after the New Year. This is the time for family, food, beer, wine and the sound of Bass Strait surf to help us get to sleep.

Best wishes to everyone for Christmas and 2018!

DT

[Dave Otto]

Looks great DT!
Enjoy your time away.

Dave

[90LX_Notch]

Nice progress DT.  Still following along and enjoying your build.

-Bob

[deltatango]

OK, sorry about the long wait but I'm finally back to the Mastiff build after a couple of "distractions". The first of these was a kit for a clone Prusa i3 3D printer which took a few days to get built, then several weeks to get working to my satisfaction. This now needs an enclosure building to keep the temperature up now that autumn is with us here but that has to wait until Mastiff is a lot further forward. The second distraction was building a stepper motor drive for my dividing heads and rotary table. This is based on Gary Liming's  "Step Indexer v. 2.3" from Digital Machinist magazine and Gary's website: http://liming.org/millindex/ . I've modified the software a fair bit to accommodate the Aciera dividing head and such features as setting fractional angle increments:



More later in the post.

The next parts are the connecting rods which are made from the rectangular bar of "high tensile aluminium" supplied by Hemingway's. I should ask Kirk for the actual specification as it is very nice stuff to machine.

The bar was milled to the outside dimensions of the conrods:



then cut into four lengths and the bearing cap screw holes drilled and tapped before separating the caps from the rod blanks and milling both sets to length:





The little end and crank pin holes were drilled, bored and reamed in a nest in the mill trying hard to keep all four parts close in dimensions:



The second "distraction" now came into its own for machining circular features into the rod blanks. The 3D printer provided the stepper motor adapter (and the cable cover on the end) and I made an Al fixture to clamp the blanks:



which allowed a ball ended end mill to produce what will become radii around the two end bosses:



One addition to the rotary table software is the ability to swing the table back and forth repeatedly through a precise angle and this was programmed to do the rounding over of the little ends of the rods. The table being set going with the cutter clear of the work and then all I had to do was raise the table to apply the cuts of about 1 mm at a time. The cutter was a new 4 mm carbide tool, and turning at around 3500 RPM. The table swing rate was ~4RPM and the next mod to the software will be to add the precise setting of this rate:



After an additional circular cut to make reducing the rod thickness easier the parts looked like:



One side of the blanks was brought to size and 1:1 copies of the drawings stuck on to guide roughing out by sawing:




The finish machining was done after picking up the end and side of the blanks with an edge finder and using the DRO and angular table settings:



I'll show more when the rods are cleaned up and fitted to the crankshaft.

Regards, David

[Roger B]

Glad to see you back on this build  That's some interesting work with the stand alone CNC rotary table   

[Kim]

That is pretty interesting - you're using the CNC like a auto-feed for the RT, with stops.  I can see that being quite useful!
And you made good use of it on those connecting rods.

Kim

[deltatango]

Roger and Kim, Thanks for the comments.

Apart from being very useful the rotary table is a learning exercise on the way to proper CNC.  I'll probably convert my Sieg X3 mill to CNC, the Aciera F3 (with DRO) is too good a machine to be modified. The "box of tricks" that drives the RT has room for three more stepper motor drivers and the Arduino Mega can run a version of Grbl that can control four axes.

The main problem with the rotary table that I haven't yet solved is measuring and correcting for backlash. There isn't very much but in the "swing" mode it can accumulate.

The final operation on the con rods was to trim the corners off the main bearing caps:



and then adjust their fit to the crankshaft. Just for fun I put the bits together:



Now I can dismantle the lot and build up the crank and parts inside the crankcase. They fit just fine in the CAD model...

DT

[Admiral_dk]

Your parts looks nice  and still following along 

The only simple solution for backlash on the rotary I know off, is to "only move in one direction" - or more correctly when moving the other way, move a bit too far and move forward to the desired point - this also works in the G-code.

A more "involved" possibility is to move the rotary enough forward so you are sure any backlash is taken up, place long pointer in the "jaws" as a "clock hand" and place a dial-indicator against it, reset indicator. Now do single steps the other way and count how many it takes before the dial moves => this is the amount that you can use as a compensation factor in the firmware.

Neither of these methods are as good as a backlash free gear, but they do come close enough for a good number of uses.

Best wish

Per

[Ramon Wilson]

Good to see you making more progress David - if there's one thing I can relate to though it's distractions 

Nice work on the crank and rods 

Regards - Tug

[kuhncw]

DT,

Nice work on the rods.  I like your rotary table modification and the way you used it.

Chuck

[deltatango]

Per, Ramon and Chuck - Thanks for the kind words! Much appreciated.

I guess the ultimate solution to the backlash problem would be a real Aciera rotary table but even if they still exist I doubt I'd want to pay the asking. Even my lovely  Aciera simple dividing head has a tiny amount of lost motion but it is probably well over 50 years old.
As it is I'll follow Per's suggestion and measure the number of steps of lost motion and burn this into the firmware. Per's mention of G-code made me think that I might abandon the special purpose firmware and get Grbl working with just the A-axis.

Thanks again -  David

[Art K]

David,
Distractions are a part of life. The rods look great. The use of a rotary table simplifies life when doing round ends on rods. When you have the Sieg X3 set up as a cnc you will do things totally different. I have had a Tormach mill for about 10 years and every time I use it is a learning experience.
Art

[steamer]

Per, Ramon and Chuck - Thanks for the kind words! Much appreciated.

I guess the ultimate solution to the backlash problem would be a real Aciera rotary table but even if they still exist I doubt I'd want to pay the asking. Even my lovely  Aciera simple dividing head has a tiny amount of lost motion but it is probably well over 50 years old.
As it is I'll follow Per's suggestion and measure the number of steps of lost motion and burn this into the firmware. Per's mention of G-code made me think that I might abandon the special purpose firmware and get Grbl working with just the A-axis.

Thanks again -  David

Just saw a F1 table on the "Bay",,,,  $2500

[b.lindsey]

Just getting caught up again and things are looking great. Good to see you back on this project.

Bill

[deltatango]

Thanks Steamer - I've occasionally seen F1 tables (and machines) at what look like ridiculous prices, F3s are easy enough to find 2nd hand in Europe but still very expensive. F3 accessories seem to be down there with hen's teeth and rocking horse droppings. A couple of weeks ago I did find 13 W20 collets and a centre for the dividing head via Gumtree for a reasonable price.

Before I could try out the fit of the crank, con rods and pistons I had to cut the clearances for the rods in the cylinder liners:



and could then put everything together and test. It was all very tight but everything rotated quite smoothly and without interferences, great! I thought until I went to fit the crankshaft timing gear. Anyone who is familiar with the Mastiff can look at the earlier picture of the crank laid out with all the attached bits and work out what I'd done wrong - I'd numbered the crank pins from the wrong end of the crank. This lead to some cursing and then more careful thought, swapping the appropriate con rods (pistons are each lapped to their own cylinders, can't swap those) minimised the amount of extra fitting that was needed and things began to go smoothly again.

Time now to go back and make a new port-side cylinder head to replace the earlier scrapper that was written off when a cutter pulled out of the collet and cut a neat hole joining the water space to the combustion chamber. This time around I had the benefit of the DRO (whatever time you spend fitting this kit is going to be repaid many times over, if you don't have one on the mill - fit it!) and a new precision vice. Copies of the drawings printed at 1:1 were glued on as a sanity check but the actual dimensions were picked from the edge of the work and the vice jaws:



holes drilled, and the water space milled out with 3, 4 and 6 mm cutters.



The last act on this side of the head was to round off the spark plug bosses on the rotary table:



The combustion chamber side followed using the same approach:





using a boring head to clean up the rounded end:



The slope between the valve clearance and the space above the pistons was formed with the work in a sine vice (more new kit that really simplified the process):



The last act was to drill and tap for the water outlet fitting and it was time to admire the part and breath a sigh of relief.




Now I can glue the covers on and move on from the bludners to having something that is starting to look like an engine.

Regards. David