Mount Trapezium

[Charles Lamont]

I think I can see a complicated and difficult way to machine it by conventional means pretty close to drawing, but I would not bother. Starting from where you are now, I would suggest turning a generous fillet radius between the large boss and the flat face already made round the small boss. The waisted sides shown in the drawing would suit the period style.

[Jasonb]

You could probably get a bit closer to what is drawn but that is likely to need version 3 as you have gone a bit too far.

After doing the holes toy could have mounted by the hole in the larger end and with a narrow tool cut down the edge of the spigot and then with the topslide set almost straight across the lathe tapered the middle down to the edge of the smaller boss. then filed the remaining bit.

Better would have been to include internal fillets where the tapered mid section meets the two bosses which is more likely on a forging or casting. Then you could do the same with a narrow round ended tool and finish around the small boss on the R/T with a ball nosed mill. Infact it could all be done with a ball nose mill slightly lowering the cutter for each increment as you move away from the large boss and then a similar amount upwards as you reset and cut upwards from the small one

There is no real need for it but would be an excuse to buy a CNC or try out 3D printing Rather than just machining what you have flat, use a small ball nose cutter if you have one and then finish on the R/T so the flat fillets out to the larger diameter. Or machine it to a step of equal radius and use a needle file to fillet it.

[Sanjay F]

There is no real need for it but would be an excuse to buy a CNC or try out 3D printing

I'm not sure I'll get the first option approved by the finance department but have I have a side project where I'm potentially looking at 3-d prinitng - watch this space!

Back to the crank, I think it was a good learning experience and given its hidden in the bowels of the engine, I'll make another incremental step and get to work with a file. I've just found a 5/32 ball nosed cutter (same size as I used for the milling) which I'll use and then file. I did also think of using a Dremel to get an approximation of slant.

I'm having trouble visualising what you are saying about using the lathe to create the slant.......

[Jasonb]

That is probably the best plan for the stage you are at.

As for the lathe, I have shown it with a radius to suit your 5/32 cutter but could do with being smaller.

1. May be easier to imagine it as a disc

2. as it would be if turned with a square edged tool

3. Better with a round edged tool

4. After milling around the small boss with a ball nose cutter, just file off the little upstanding bits

5. Same from the other side

[Sanjay F]

I got it, thank you, definitely one for the next one of these I have to make

[Sanjay F]

Okay, I think I'm done with the crank, it's not perfect but I think it'll pass.....and my fingers are worn down from filing 

[Michael S.]

This is truly handmade! 👍

Michael 🍻

[Sanjay F]

I just wasted this morning's work, but want to learn from the mistake. I'm making the outer bearing block and was milling this vertically in the vice as seen in the picture. I look it to depth then moved the cutter laterally to get the correct width in 0.010" increments

1. I snapped my the cutter which wasn't too bad and damage to piece minimal
2. Changed cutter, this time the work jumped in the vice and this was terminal

I think I should have had the work laying horizontally (see pic) with the cutter moving in the x-axis so there was less material being cut?

[Jasonb]

Was that at the start of the cut eg moving the table towards you or at the end eg moving the table away from you.

All other axis and quill locked?

Aluminium or steel part, hard to be sure from photo

How much metal is in the vice below th etop of the jaws

Remind me what mill you have again and can you take a photo showing the whole of the table with vice

[crueby]

I've had that happen, usually since the part was not held well in the vise, and I found that the bar stock was not as parallel sided as I thought. A lot of bar stock has a bit of curve to the sides, sometimes out in the center, sometimes out at the edges. Or the cut end has a bur sticking out. I've gotten in the habit of clamping stock in the vise, then giving the end sticking out a good hard shove with my thumb to see if it pivots. One trick that can help is to put pieces of paper either side of the bar, so the vise crushes it down as it is tightened, taking up some of the un-even-ness in the bar. On my small machine, not as rigid as larger machines, have also learned to use smaller diameter end mills and take lighter cuts so there is less force on the part. Also I dont try to cut through full depth, but take multiple passes, lowering the cutter more on each pass. Once it starts to move in the vise, its game over, and looks just like yours does.   

[Sanjay F]

see answers below next to your quote......

Was that at the start of the cut eg moving the table towards you or at the end eg moving the table away from you. - The first time when the cutter broke I was machining the LHS upright table moving towards me. Second time when the piece jumped I was doing the RHS upright table moving away from me -  I always get confused about the direction of travel of the cutter in relation to the movement of the table

All other axis and quill locked? - all locked other axis and quill locked locked moving along y-axis (back to front)

Aluminium or steel part, hard to be sure from photo - mild steel

How much metal is in the vice below the top of the jaws - 1.25" (more than half it height)

Remind me what mill you have again and can you take a photo showing the whole of the table with vice - its a Warco WM16 (see pic)

[Sanjay F]

I've had that happen, usually since the part was not held well in the vise, and I found that the bar stock was not as parallel sided as I thought. A lot of bar stock has a bit of curve to the sides, sometimes out in the center, sometimes out at the edges. Or the cut end has a bur sticking out. I've gotten in the habit of clamping stock in the vise, then giving the end sticking out a good hard shove with my thumb to see if it pivots. One trick that can help is to put pieces of paper either side of the bar, so the vise crushes it down as it is tightened, taking up some of the un-even-ness in the bar. On my small machine, not as rigid as larger machines, have also learned to use smaller diameter end mills and take lighter cuts so there is less force on the part. Also I dont try to cut through full depth, but take multiple passes, lowering the cutter more on each pass. Once it starts to move in the vise, its game over, and looks just like yours does.   

I wondered about the depth of cut hence thinking next time I'll lay the piece horizontally, it was my favourite 8mm Guhring end mill which snapped too. I'll try the paper idea next time - it took ages to get the stock to size and I don't want to have to do it all again if possible! 

[Sanjay F]

I don't know if it makes any difference but the speed of mill the was 750 rpm, its the first time this has happened to me so rather puzzled.

I've now cut new stock to size and will drill some holes to commence the slot for the bearing brasses, after which I'll start milling again, I'll try laying it horizontally, with the cutting area protruding out of the vice, I may be able to provide extra support with a pair of mini jacks under the corners? Maybe also a small cutter?

[Charles Lamont]

That looks like a 2MT Autolock chuck. If it is, and just in case you did not know, once the drawbar is tight, the damping ring at the top of the chuck can be screwed up firmly against the spindle nose, which considerably improves the overall stiffness.

[Jasonb]

One thing you have to watch with those "precision" type vices is that they tend to offer less grip if the screw is a long way into the bar. This is because the angle of the screw become steeper so you are pulling the jaw more downwards than towards the work. Only time I have had work move when simply cutting is with these type vices. Related to that some have a screw that is too long and bottoms out on the mill table so you may think you are tightening it right up but the resistance you feel is the screw hitting the table.

If you do cut it laid flat then there is no reason to have it sticking out the side unless there is material to come off there rather than just the middle cut out you show. You will also end up with rounded internal corners

10thou at full depth should be OK, I do it myself. Maybe drop to 5 thou particularly if steel.