DIY CNC-Valve seat cutting machine: Air-Cushion vs. Fixed spindle?

[denhen89]

Hello Guys,
i am Denis and its my first post here. I was searching for informations about Serdi type cnc valve cutting machines, espacially about the air cushion spindle system and i found some informations here, so i thought i might try to get some help from you.

The main question: If you would do max 4-6 cylinder head valve cutting jobs in a month (or generally rebuild 4-6 complete engines a month), would you still recommend a Valve cutting machine with Air-Cushion type spindle that is self aligning or a fixed spindle and align it everytime to the pilot?

Now some informations: I am planning to rebuild about 4 engines a month and if it works out well, later more if possible. I am not a machinist, and i never have rebuild engines (only repaired without machines), but since 2017 i am very interested in machining and cnc. I have build 4 CNC machines - one large and precise cnc router as well as a very price and heavy lathe that i conversed to cnc and some other machines, so i believe i can also build a valve cutting machine by myself, but i dont like to buy tooling for each profile, thats why i want to build a Serdi Stronik/Serdi Profile type machine.

I am sure i will have no big problems to build the U-axis head where the cutting tool moves (currently creating CAD drawings), but when it comes to the Air-Cushion Spindle system i see some problems, or at least i believe it will not work out perfectly the first time and will take some prototyping.
Thats why i am asking you if it makes sense to try it out, or just use a fixed spindle and align the valve seat everytime with the pilot in the valve guide.

The valve cutting machine will be actually a "standard" fixed-column/portal type cnc machine, with linear rails, on which i want to also do cylinder boring jobs and block/head surfacing. I dont plan to use air cushion for the axis movement or the bed. The cylinder head should be mouted to a common rotating head mount that will be fixed to a table that moves from left to right. About all the other axis that will move on linear rails i might write in another posts, but for now it would be very interesting to me to know if it even makes sense to think about the air cushion spindle system. It would safe me a lot of time and even money if would go with the fixed spindle system. I have 2 very precise new lathe/milling spindles here that i could use for boring, surfacing, valve cutting and similar jobs.

Okay, i stop for now. Its late.
Thanks in advance and best regards, Denis.

[williamsmotowerx]

You will need air float table. Indexing each seat by indicating takes way too long.

Look for an old seat and guide machine with air table and use that for your base

[denhen89]

Thanks for your answer.
So, you actually mean the table should as well have air float, or you answering my question if i should use air float/cushion spindle vs. fixed spindle position?

[williamsmotowerx]

Fixed spindle, your design.

Use an old air float table.

I've built cnc machines too. Anything can be done with time and money. Sometimes it's not cheaper to do it yourself.

I've cut seats on a bridgeport for years. It cuts a decent seat.... but it takes way too long... and yes I've built fixtures to speed up process.

[modok]

The serdi ball-joint mounted spindle is a lot easier if doing canted valve heads.
Guides only need to be within a degree or two of vertical, not perfectly vertical.
Will you be doing heads with canted valves?

If your spindle is always perfectly fixed vertical then that means you need to get each guide perfectly verical too. Not hard to do with most heads, but a real pain with others.

[williamsmotowerx]

The serdi ball-joint mounted spindle is a lot easier if doing canted valve heads.
Guides only need to be within a degree or two of vertical, not perfectly vertical.
Will you be doing heads with canted valves?

If your spindle is always perfectly fixed vertical then that means you need to get each guide perfectly verical too. Not hard to do with most heads, but a real pain with others.

The fixture on the air float table will cant.

Machine must be level. Spindle must always be 90 degrees to level. Then you put a level on pilot, use fixture to move head around until pilot is 90 to level. Then you use air float table to position head in center of Spindle

[modok]

Are you telling me how to do it? Lol

Why can the spindle designed to tilt 5 degrees if it has no purpose hot shot?

[denhen89]

Again, thanks for your answers which are pretty helpful for me.

Its a good question if i will do a lot of canted valve heads.
I will most likely repair/renovate standard passenger car engines, e.g. 3-4 cylinders but as well 6 cylinder engines, so i would like to have a universal setup.

Fixed spindle, your design.
Use an old air float table.
I've built cnc machines too. Anything can be done with time and money. Sometimes it's not cheaper to do it yourself.
I've cut seats on a bridgeport for years. It cuts a decent seat.... but it takes way too long... and yes I've built fixtures to speed up process.

Machine must be level. Spindle must always be 90 degrees to level. Then you put a level on pilot, use fixture to move head around until pilot is 90 to level. Then you use air float table to position head in center of Spindle

Good to know and that would make my life a bit easier if i dont need to build the air cushion spindle, but i would love to try to build one, because such spindle would also make the work a lot easier i believe.

One question to the air float table: The fixture on which the cylinder head is mounted is floating on the table while there is air pressure, but when air pressure is off, the fixture is then fixed to the table, through electro magnets?

[matthewest91]

Interesting thread! Keep the info flowing !

[williamsmotowerx]

Are you telling me how to do it? Lol

Why can the spindle designed to tilt 5 degrees if it has no purpose hot shot?

Original question is a DIY seat cutting machine. I'm not telling you to do anything. Building a rotating spindle, or air float spindle for a DIY is bringing in complications that aren't necessary

[modok]

Sure I'll agree with that.
It's hard to make a machine to do everything.
Imo four or less car/motorcycle it makes sense to float the table.
L6 or flathead, big deisels, better to float the spindle.

So maybe i'd go with a parallel floating spindle designed for four cylinders. To to longer heads, just move the workpiece over. Could have different fixtures to hold the oddball heads.
The majority of work will probably be parallel valves.

[denhen89]

Hello Guys,
i will not reply to all answeres and all infos you gave already, but you helped me out already a lot.
Its true that building the air floating spindle might not be very easy, but due to the fact that i have a very precise CNC Lathe that is capable of turning such big stock as the "ball sphere" or the housing of the Ball sphere, i would still like to try it out. I will design the "ball sphere shaft" and housing as soon as i am ready with the U-Axis, so that i know what diameter it has to be.
BUT, i just got a reply from a chinese seller/manufacturer of valve seat cutting machines and i got already the price for the Sphere (you can see it here: https://ab-engine.com/img/serdi/serdi_sphere.jpg), but i now asked if its possible to also buy the housing for it. If so, i might be able to solve the biggest problem in case i dont manage to build that air float spindle system.

So, even i now understand due to your help, that the most jobs i can do quiet fine without air float spindle, i would still like to have it and build the machine so that the machine is universal as possible. Another thing is, if i have the air float spindle, all the geometry of the machine does need to be precise, so i might even think to build the machine just for the cylinder head jobs and with floating ways instead of linear rails. Its cheaper to just get the surface flat for air float instead of machining many surfaces for the linear rails and also setting up all axis to each other, which i like to do, but it takes time, which i would like to safe, especially because i have already a huge cnc router that can cut steel, so another miling machine isnt really necessary and Block boring/honing i could also do on the cnc router in future with some updates.

Currently i am facing a problem so i need your advise: Serdi and Newen uses hydraulic chucks for the pilot. I could do the same, but the hydraulic chucks that i am finding on the internet have quiet a big diameter of mostly about 48mm (1,8897 inch), and therefor i would need to make the housing of the U-Axis bigger which isnt really what i want, because i am trying to build it as compact but rigid is possible.
I saw that the standard (non cnc) valve seat cutting tool holders hold the Pilot by a set-screw, like "weldon type holders". Do you think that its a alternative to the hydraulic chuck? I havent checked the weldon type tool holders yet, so i might find out that the diameter of such holders will be also too big for my current U-Axis design.

If you guys are still interested in what i am trying to achieve then i will try to write some updates from time to time.

[modok]

Why would it be necessary to strongly lock the pilot into the spindle? There should be no real turning torque on the pilot.
the set screw just keeps it from falling out, that's all that is needed.

If the pilot did seize in the guide it would be preferable for it to spin in the tool holder rather than break off.

[denhen89]

That makes sense what you wrote, but i am not sure about the run out at the end of the pilot when i just make a 9.52 (3/8 inch) hole with a set screw as a holder for the pilot, but i have found already a solution to this problem.
Maybe i am overthinking a lot when it comes to the tool holder, due to the fact that i never worked on such machines like Serdi. For me its important that its very rigid and precise spindle assembly and the U-axis has to be stiff, but also i want it more compact than the Serdi Profile head.

[BCjohnny]

Now some informations: I am planning to rebuild about 4 engines a month and if it works out well, later more if possible. I am not a machinist, and i never have rebuild engines (only repaired without machines), but since 2017 i am very interested in machining and cnc. I have build 4 CNC machines

I think you are trying to run before you can walk ...... it makes no sense to build a CNC type machine to do less than half a dozen heads per month, unless the ultimate object is to just gather information to build and market such a machine, and thus not actually process heads yourself

Having never 'machined' a head yourself I'd suggest you tool up a 'Bridgeport' type machine and learn for yourself all the ins & outs of the complications you'll run into holding concentricity, TIR, finish etc etc, and then apply anything learned that to your CNC venture ......

[Much like many people produce better results on an automatic hone having 'hand honed' first]

Plenty of info on here how to go about tooling up and using a BP, and more than adequate for the initial volumes you're anticipating

Valve seat cutting is probably the single most discussed machining subject on ST, and there are many & varied valid opinions on how to go about it from machinists who probably have a collective experience of thousands of man years 'perfecting' their art ...... so fill your boots

CNC will introduce it's own issues, and I'm not aware of a single one who thought going that route as the initial effort was a practical idea

JMO