Designing an engine

[petertha]

I'm no expert but I found backing out & clearing chips often & WD40 makes for happier aluminum drilling. Crappy, dull, knockoff bits are a non-starter IMO.

Another thing I tried when faced with relatively deep & small diameter holes in aluminum is parabolic profile. Seem to work better than regular bits & straighter hole. I tried Titex brand HSS uncoated, so far so good. They are more spendy though.

http://blog.cnccookbook.com/2013/09/06/parabolic-vs-standard-flute-twist-drills/

I know some people regrind the lip angle for grabby materials & including brass apparently. I don't have those facilities so its a check-book solution.

 

[mu38&Bg#]

A common common problem with drilling is not feeding fast enough. What is your feed and speed? Drilling in aluminum needs .001-.002" per flute per rev. If spindle speed is high, feed rate can be pretty high. Peck drilling is need to clear chips. Without coolant you have to start pecking at maybe as little as 1.5-2 diameters deep. it really depends on what your chips look like. Sometimes chips clear nicely, other times they don't. Bright HSS drills work best (until you step into carbide), any tialn or altin coating containing aluminum will want to stick. Cheap drills are a waste of time unless you can resharpen them well. Drills previously used in harder metals should be resharpened for best results in aluminum. I try to use four facet drills and resharpen them with four when being used for aluminum.

Greg

 

[Metal_slicer]

A common common problem with drilling is not feeding fast enough. What is your feed and speed? Drilling in aluminum needs .001-.002" per flute per rev. If spindle speed is high, feed rate can be pretty high. Peck drilling is need to clear chips. Without coolant you have to start pecking at maybe as little as 1.5-2 diameters deep. it really depends on what your chips look like. Sometimes chips clear nicely, other times they don't. Bright HSS drills work best (until you step into carbide), any tialn or altin coating containing aluminum will want to stick. Cheap drills are a waste of time unless you can resharpen them well. Drills previously used in harder metals should be resharpened for best results in aluminum. I try to use four facet drills and resharpen them with four when being used for aluminum.

Greg

Thanks for the info Greg. I was break chip drilling after every 0.025" at 2800 rpm and the bit was coated I believe with tialn. I ended up manually drilling with a different bit making longer chips because I believe the smaller chips were building up and not able to clear out of the hole. Bottom line I did several things wrong here.

The good news is that I was able to complete the operation and move on to the other CNC operations and was able to finish the entire bottom of the valve cover today. I need to flip over the cover and do the final operations. I took some pictures with my cell phone but it is so out of focus so I might have to wait until I am finished so I can take a picture with my DSLR camera. I don't want that camera anywhere near fling chips and oil.

 

[Metal_slicer]

Valve cover completed. I was not happy with he way the groves turned out. I used an 1/8" 4-flute end mill and used an engraving operation. Oil didn't make a difference. I will try to hand finish this to make it better. Any tips for the grooves?

For the most part everything else turned out ok.

 

[petertha]

Is the end mill slot raggy on one side but cleaner/better on the other? Might be a direction/rotation thing? (climb milling etc). Maybe just a finishing pass is required with this in mind?

 

[Longboy]

Those small diameter end mills flex and load up with chips easy galling the sides of a groove cut. You are into a hand finish now. I measured my 12inch single cut file and its .135in wide. You can drag it at an angle along the groove length to smooth somewhat or oversize the width with the end mill so you take only a one side cut and reverse to other side. A brass or steel wheel brush for electric drill can carve up some of the vertical wall mess and whatever horizontal top surface ends up with brush marks can be easily be sanded and polished out. Try a clean-up with a groove on some scrap aluminum.

 

[Swifty]

I always use WD40 on aluminium, a spray can is handy, but I recently bought a 4 litre bottle which I decant into a smaller container and use a brush to apply, stops aluminium from sticking to the cutter. A lot depends on the aluminium that you are using, normal extrusion is usually fairly soft and sticky, I'm a great fan of using structural plate aluminium, a harder grade and great for machining.

Paul.

 

[Metal_slicer]

I have a question about what to do for the valve guides? would drilling the guides be good enough or should I ream them? The cylinder head material is C360 brass.

 

[Swifty]

I would ream them, a close fit on the valve shaft is required. Imagine when the inlet valve is open, if there is too much clearance between the shaft and hole, it would suck in air, instead of the correct fuel mixture through the carby.

Paul.

 

[Metal_slicer]

Thanks Paul, I appreciate your input!

 

[Metal_slicer]

Things are starting to stack up... I really need to try to refinish the valve cover groves. The camera is giving it to much justice!

I still need to cut the valve seats and ream the valve guides which I will need to order. If I ream the guides for 1/8" what size drill do you recommend I use?

 

[Swifty]

I use a drill about .004" undersize before reaming 1/8" holes.

Paul.

 

[Metal_slicer]

Sorry guys I don't have any photos of my progress but here is what I have done the past few days.

1.) Drilled head bolts, rocker arm studs, push rod holes and valve guides
2.) Drilled camshaft bore. Still need to make a 5/16 flat drill to make the camshaft bearing pockets

I found an error with the valve cover. I did not account for head bolt clearance so I will need to re-machine the valve cover to fix this problem. Error with exhaust ports have mounting screws clipping the ports. Not to big of a deal, its good the intake ports are free from any screw holes. Last concern is the lack of head material left for the valve stems. I have about 1/8" thick brass for the valve stems.

Pictures coming later...

 

[Blogwitch]

MC,
A little late I am afraid, but your problem with cutting slots is a very basic one.

If you want a decent finish and size for a slot or cutout, you never start off with the correct sized cutting tool, especially in the smaller sizes as they flex too much, and will usually cut oversized.

Say I was cutting a 1/8" (3.2mm) slot, I would use a 3mm slot drill to rough out first, leaving a couple of thou to remove on depth. Then, when you follow down with the correct sized cutter set to correct depth and running at fairly high speed the chip load is greatly reduced to almost nothing and you will end up with a perfect sized and smooth finish on the slot.
I know it takes twice the operations and time, but hey, we are not in a race to finish anything, and you would certainly appreciate the smoother finish, and you will pick up a lot of the time wasted by not having to do so much cleaning up work.

John

 

[Metal_slicer]

I did a practice valve seat cutter copy based on Steve's design. I did it with aluminum to run through the operations before trying tool steel. I'm not sure if it would be cost effective since I would need to get a torch outfit to harden the tool. It may be better if I buy a 45deg off the shelf cutter, however I like the valve stem guide pin on the custom design. No sure...

 

[Metal_slicer]

Here are some pictures of the cylinder head with all the holes drilled for valve cover, rocker studs, valves, and push rods. I didn't plan on making separate valve guides, but there is just not enough material in the head to serve as valve guides. I have not cut the seats yet either. I have a temporary aluminum retainer that does not have an e-clip, it is resting in the valve stem grove for the purpose of this photo shoot. I really didn't want to make any press fit parts but I might as well give it a shot. About how much of an interference fit will I need for the inserts? Comments welcome.

 

[Swifty]

There are various charts for different fits, but one thing you have to keep in mind, is that in a hole of lets say, 0.5000", a pin of the same diameter will be a tight fit. What I normally do is make the pin the same dia as the hole and put a drop of loctite on as well, more as a lubricant than to hold the pin in.

Paul.

 

[Metal_slicer]

I did some more work today. I cut the roller tip rockers out and parted off 4 303 stainless roller tips. I still need to mill the mid section of the rocker arm for the 1/4" bearing. I also need to hand finish the parted off roller tips. Here are some pictures of today's session in the workshop.

 

[Metal_slicer]

More work done on the engine.

 

[Metal_slicer]

Here are two more photos of the rockers mounted. I am going to need to make valve guides because there is not enough support in the head the way it is now.