JV Puleo

My 1910 Mitchell "parts car" project

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Posted (edited)

Today I drilled and reamed two 1" holes in the block. I reamed the holes in order to get the most accurate surface possible to center the spindle for the boring head.

 

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The centering worked fine. I had a strange problem with the milling machine, one I've never had before but I think that's taken care of now. The holes were bored to 1.510.

 

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And... they didn't fit or at least didn't fit as precisely as I'm looking for. I think my measurements are fine but I now think the various operations weren't done in precise enough manner. The more operations there are - and the more tools you use, like the vise's that held the part in both the drill press and the mill, the more it will vary a few thousandths. I could use this part - the holes are about .020 too close together but since I have to make the other three, it's little more work to make four more. This time I've eliminated the vise from the equation and clamped the piece directly to the drill press table to drill the center hole. I've also used this long center drill to start the hole rather than the transfer punch I used the first time. I am certain this is more accurate. The center drill is exactly the size of the reamed hole in the gage block while the angle plates the pieces are clamped between make certain everything will be in line.

 

 

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After all the center holes were drilled and reamed I repeated this operation for the lifter holes but this time I put the 7/16 transfer punch in  the center hole so that the pieces cannot move in any direction.

 

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Edited by JV Puleo (see edit history)
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Joe, you can call me 'thick' if you like, but what is the part you are making and what is it for? Whatever it is, it is very nicely machined.

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You don't recognize it because it looks nothing like it will when done - and about 3/4 of the metal is removed. they are the "hold downs" for the lifters... bolt to the crankcase and each one holds two lifters in place.

 

 

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Thanks for explaining. My excuse is that it was 6am this morning when I read your post!

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This is one of those jobs that is turning out more difficult than I anticipated. I've spent yesterday and today fiddling with ways to do it. I'm finally making some progress. This is what I was aiming for...

 

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The stock is too thick - I changed the design after I'd bought it and, of course, most of it will be removed. I think about 2/3 of this will be gone by the time I'm done.

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In that case, cut it in half and you will have two!

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Unfortunately, it's only 1/4" too thick. I think this will go down as one of my over complicated designs. They will be nice though - if I can do it.

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Believe it or not, this represents most of today's work. At least they fit correctly. The next step is to tidy up the hole in the center. It is critical that it be in the exact center because I will be milling it round using the center as the registration point. For that I need a long 1/2" end mill which is supposed to be delivered on Monday. Until I get it, I can't move the vise or the table on the mill because I don't want to disturb the alignment.

 

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Jeff,

Just before I left tonight I decided to mic the web between the two holes... three were .858 and one was .859 so it looks as if my method was even more accurate than I'd hoped for.

 

jp

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Joe,

 

I am trying to become more accurate with my machining after following your posts. Is it possible to show us how you measured between the two holes? I have problems when I try to measure between two curved surfaces. My measurements never seem to come out the same each time I measure the same part, especially when trying measure a hole in a bore, when I am trying to get it to a certain size in the lathe. To overcome this problem I tend to make a 'plug' of the correct diameter to try in the bore.

 

Mike 

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Posted (edited)

It isn't easy...

One took I've found very useful is the telescoping gage - for measuring the inside of a hole. They are fairly expensive new but readily available on ebay used and reasonably cheap. The arms spring out and you can measure them with a micrometer or dial vernier.

 

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As far as setting the distance between the two holes, moving the table on the mill proved to be, by far, the most accurate. The first hole was located - the dial at the end of the table set at zero and when the first hole was bored I just moved the table. None of my other ideas worked as well. The trick here was getting the hole in the middle in the right place and I was not 100% successful. I will correct that on Monday or Tuesday but if I had to do it again I'd have set the piece up in the mill, drilled and bored one hole then moved the piece down and done the other. I would not put the hole in the center until I was done boring the large holes.

 

jp

Edited by JV Puleo (see edit history)
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Thanks Joe. I have just realised I do have a set of telescoping gauges  Perhaps I better start using them!!

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Posted (edited)

Our local weather report predicted rain today so I put the charger on my lawnmower and came into the shop. Of course, it hasn't rained and now the prediction is that it will rain tomorrow. So... I cleaned up the milling machine (I hate working in a pile of chips) and gave some thought to the rest of the job. One problem I have is that I've outsmarted myself a bit. The original lifters were kept from turning in their holes by a small dowel pin through the rim of the housing into the crankcase. I couldn't think of a way to drill that hole accurately - since none of the measurements are consistent on this engine. So, I designed a system where each pair of lifters would lock to each other. Since then, I've thought of a way to do it but I'm committed to making the pieces for the system I designed if only to keep everything looking complete. What I wanted was a cross-shaped piece on the bottom of the hold-down that would engage a notch in each lifter with a straight section in the middle that would be up against the lifters.

 

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I'm still thinking about how to make these and attach them to the lifter hold-down but in the meantime, I set up the next operation - putting the hole for the hold-down stud directly between the two big holes. Were I to do this over (God forbid) I'd have put this hole in last but this will work too. The first step was to locate the hole exactly. I did that by finding the edge of the first big hole. This is a piece of 1/2" ground stock, held in a collet, painted with layout fluid.

 

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I start the mill and move the table very carefully until the edge just scratched the red dye.

 

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Then the table is lowered and moved over .250 (for half the thickness of the ground stock) + .4025 (half the distance between the two holes). This should put the hole directly in the center give or take .001 which is plenty accurate enough. I use this system for edge finding even though I have a "store bought" edge finder as it seems so much easier. It is probably not aerospace accurate but more than good enough for automobile work.

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Edited by JV Puleo (see edit history)
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To my relief, the long 1/2" end mill came in this morning so I was able to fix the center hole.

 

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Then it occurred to me that all I had to do to center the remaining holes was to put the piece of 1/2" stock in the collet and push the piece over until it touched...which made doing the remeining holes a cake walk.

 

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The next step is to mill abut 1/2" off the ends. This is to get a surface to hold the piece down to the rotary table. I confess I hadn't thought about this ahead of time and I'm hoping that there will be enough friction between the piece and the top of the table to keep it from moving.

 

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All done... tomorrow I'll set up the rotary table and it will be a lot clearer what I'm making here.

 

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I set the "test piece" in the rotary table this morning and began milling.

 

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An inch of the material is removed around the boss in the center.

 

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Then it goes in the lathe to have the ends turned off.

 

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This is what it should look like. It's obvious I didn't center it perfectly so I'm glad I had this one to experiment on.

 

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And on the engine. The boss in the center will be reduced but I need the studs that will hold them down first as I want to use acorn nuts on top and need to adjust the height to the studs.

 

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The prototype was well worth the trouble. I re-centered the rotary table using a different method - still not perfect but much better. Then I decided to bite the bullet and use one of the pieces with the holes in the right place. I followed the same routine but this time, while the centering wasn't perfect, it was closer. After I'd machined the part I decided that there wasn't enough clearance between the lifters and neck of the hold-down so I put it back in the lathe on an expanding mandrel and turned the neck down to 3/4" - which is actually the dimension I'd intended to use when I designed this. This trued everything up and I'm reasonably pleased with the result.

 

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The radius at the base of the neck is made by using a 1" end mill with a 1/4" radius. I bought 3 of them to use when I make the connecting rods so I'm hoping I don't wear them out before I get to that job.

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8 hours ago, JV Puleo said:

The radius at the base of the neck is made by using a 1" end mill with a 1/4" radius.

 

Joe, when you did this machining did you rotate the rotary table by hand to remove the metal? Sorry for the questions but I am trying to learn from your excellent posts.

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Yes. I don't have a powered rotary table. Actually, I've only seen them on bigger machines like a P&W vertical shaper. I think you might be able to power a rotary table (I know you could power a dividing head) on this machine but it would require all the extra bits it originally came with and that I've little chance of ever finding.

 

j

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Thanks for that. I wasn't sure if you rotated the table or plunge cut and kept moving the table around. I shall now dig my rotary table out from where it has been in the cupboard for the last 10-years and put it with the mill for future use. Yet another machining tip I have learnt from your excellent posts. Mike 

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You could never go that deep and rotate the table - at least not with my machine. I'm not sure what the optimum depth of cut for a 1" end mill. I seem to remember reading somewhere that it is 1/2 the diameter of the cutter but I didn't even try that. I took these down .050 at a time.

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Today I milled the remaining three pieces. I decided to go only 3/4" deep because with the neck in the center turned concentric with the center hole I can hold them in a collet and it is a lot easier to take the thickness down from the bottom.

 

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Then I put them in the lathe and removed the excess material on the ends. Tomorrow I'll reduce the thickness of the bottom end to 3/8" so they match the brass rings on the lifters.

 

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Your thinking, planning and execution are all great!  Nice end results!

Al

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Today I reduced the base of the hold-downs to 3/8". Had I made them from thinner stock, this would have gone faster. Still, the finished height is 1". I would have used 1-1/4 thick stock if I had one of these finished ones to copy but I'd bought 1-1/2" and didn't want the expense of buying it again. Still, it probably didn't add much time to the job. The reall time killer is the experimental stage - doing something you've never done before is like that.

 

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With that done, I put them back in the lathe and trimmed the tops so that they are all identical in height. This is important because I want to use acorn nuts to hold them down so I have to get a consistent length for the studs - which I'll also have to make because I can't seem to find any that fit my dimensions exactly.

 

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there is still a little more to do but I'm waiting on the materials. Tomorrow I'll probably go back to the oiling system.

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Hello Joe,

Yet another step on the road to recovery of your Mitchell.

Al

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