# Fly cutting on the mighty comet



## sasanifab (Mar 10, 2021)

So I build engines on the side, more specifically the 4g63 and Honda Variants. I took it upon myself to try to mill the head and the deck of the block. The issues I have I believe are related to rigidity. The iron block actually came out perfect. I’m having more issues with the head. I think it may be due to the fact that I dont have the proper   Fixture for it and it’s rocking. If you look at the surface finish it looks scalloped. I’m looking for a mirror finish. Ive tried brazed on tooling and indexible tooling. Maybe hss ? What’s the best for aluminum ? What are guys doing to add rigidity to their mills ? This is a Mighty comet just over 2000lbs. I was thinking about adding sandbags to the base?  I’m even considering bolting it to the concrete


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## Mitch Alsup (Mar 10, 2021)

I would recommend Cobalt HSS with a tip radius of just a couple of thou and a feed rate of a couple of thou per rev. I see a lot of head/tool deflection on the interrupted cut on the head. The small tip radius with a shallow DoC and a slow feed rate will take a lot of the forces that cause deflection out of the picture. Also note: a bit of "character" on the head will help it grab the gasket.

But you need machine jacks under the head to support it from deflecting under the loads of machining.
You may or may not need to stiffen the machine to the floor.

While 2,000 pounds is heavy for a mill, it is chicken feed to machines designed to machine heads.


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## Ulma Doctor (Mar 10, 2021)

you are getting chatter!
as Mitch said, low doc's - large radius on the tool
you didn't mention whether you were machining wet or dry- machining wet may improve the surface finish
tool speed and machine wear, could be factors too


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## sasanifab (Mar 11, 2021)

Ok that’s what I thought , the iron block came out perfect, the block was bolted directly to the table and is obviously a lot more rigid. I need to come up with a good way to support the head


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## Mitch Alsup (Mar 11, 2021)

sasanifab said:


> Ok that’s what I thought , the iron block came out perfect, the block was bolted directly to the table and is obviously a lot more rigid. I need to come up with a good way to support the head



5-10 machinist jacks.


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## tq60 (Mar 11, 2021)

Block is good so no worries about weighing down mill.

How are you anchoring the head?

Bolts through spark plug holes maybe?

Aluminum requires a whole different cutter and "style "

Sometimes very slow speed whole sometimes fast.

The deep cuts tell me something is either moving or buildup on The cutter.

Dawn makes good coolant as it is slippery and cheap.

Garden sprayer makes application easy.

Sent from my SAMSUNG-SM-G930A using Tapatalk


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## FOMOGO (Mar 11, 2021)

Cylinder heads are usually mounted to the mill table by front and rear surfaces of the head. Here is a good example of a homemade setup. Mike             


> I started to get into the cylinder head work a while back, and since I'm a cheap bastard...I made this rollover fixture.
> 
> 
> 
> ...


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## sasanifab (Mar 12, 2021)

I found an awesome cmt insert that cuts likes butter, I just need to purchase an appropriate jig for the head


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## jakes_66 (Mar 12, 2021)

I've been surfacing aluminum cylinder heads with a flycutter on my South Bend VMM.  Check the gibs on your ways for proper adjustment.  This made a big difference on reducing chatter and improving surface finish for me.


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## sasanifab (Mar 12, 2021)

jakes_66 said:


> I've been surfacing aluminum cylinder heads with a flycutter on my South Bend VMM.  Check the gibs on your ways for proper adjustment.  This made a big difference on reducing chatter and improving surface finish for me.


I was using a half ass way to secure the head to the table , the block finish came out perfect imo. I’d assume if my Gibs were out too I’d have issues with the block too no ?


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## jakes_66 (Mar 17, 2021)

sasanifab said:


> I was using a half ass way to secure the head to the table , the block finish came out perfect imo. I’d assume if my Gibs were out too I’d have issues with the block too no ?


A couple of things, surfacing iron parts is very different than surfacing aluminum.  I use high speed steel with an aggressively positive rake angle and WD40 for lubrication on aluminum.  Good fixturing is challenging, but it is a *must *for aluminum cylinder heads. Minimal tool stick-out on the flycutter will reduce chatter on the interrupted cuts as the tool passes over the water ports, bolt holes and combustion chambers.  After zooming in on your photo I can see your chips are not cleanly cut, they are rolling over and clinging to the edge of the combustion chamber in the direction of the cut.  Try the aggressive rake angle and hone the tip of your HSS.  Try WD40 if needed.

I recommend brazed carbide (dry) for the cast iron, usually C1 thru C4 grade does the trick.  Cast iron naturally absorbs vibration, therefore you won't notice as much chatter in the deck of your block.  I still think I see a 'halo' around one side of each cylinder in the direction of the cut.  This could be a tool 'bounce' in the direction of the interrupted cut.  I think your machine is capable of decent cuts on these parts, but it *must *be adjusted properly.


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## sasanifab (Apr 3, 2021)

This is the jig I purchased , I
 Going to add some supports on the other side but it’s pretty rigid


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