Author Topic: Fitting a piston for F2C engine  (Read 2863 times)

Offline Neil-Lickfold

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Fitting a piston for F2C engine
« on: January 11, 2019, 05:08:02 AM »
This is trimming a piston to  fit for an F2C diesel team race engine. The crown has a short taper, about 0.5 deg per side for the crown thickness of about 2mm.
The main part of  the piston is just parallel turned. At .5 deg angle of the topslide, every 0.05mm movement is 1 micron in diameter cut. The only PCD inserts I have found to be any good for this sort of work has been the positive geometry PCD inserts from Summitomo in Japan.

Offline Niels Abildgaard

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Re: Fitting a piston for F2C engine
« Reply #1 on: January 11, 2019, 06:27:01 AM »
Thank You for some very interesting pictures.
The holy grail has been to lap piston an liner together and You do it by plain turning.
How do You aply feed fine enough?
When do You use three jaw and when ER collets for holding mandrel?

Offline Jasonb

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Re: Fitting a piston for F2C engine
« Reply #2 on: January 11, 2019, 07:09:06 AM »
Nick the last photo looks to have a much better finish than the one 3rd up from bottom, have you done something other than turn to get to the last photo? My thinking is that if magnified a fine turned surface is a fine screw thread, lapping tends to flatten the crests but just turning to size does not.

Also do do you find that those inserts will repeatably take off 1 micron for 1 micron advance of the tool, other inserts would tend to just run with that shallow a cut.

Finally how do you measure the bore and OD of the piston to know there is X microns to come off?

J

Offline Ramon

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Re: Fitting a piston for F2C engine
« Reply #3 on: January 11, 2019, 08:47:44 AM »
Thanks for describing your technique on this method Neil.

I was surprised to find you are using tip tools for this op - which goes to prove (to me) just how sharp tips are compared to my day.

You don't say what the material is - it appears to be steel as opposed to my usual use of cast iron.

As Jason refers to,  a lapped finish removes most if not all of the machining marks so I can only assume your surface finish is very fine - by usual standards that is - what feed rate are you using ?

Once you have the fit in the bore at the lower end do you have a degree of taper in the liner to work tighter at the top end? If so how did you achieve that.

Sorry for all the questions but 'if you don't ask.....

Regards - Tug

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(a very apt phrase - thanks to a well meaning MEM friend)

Offline Neil-Lickfold

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Re: Fitting a piston for F2C engine
« Reply #4 on: January 11, 2019, 10:59:44 AM »
So these pistons are made from RSA 444 a 30% silicon material from the RSP company in Holland.
The pistons are on mandrels, that allow the liner to be fitted over the piston to near TDC.
The back part of the mandrel is about 0.1mmin diameter smaller than the finished diameter of the piston.
Sometimes I have the mandrels in an ER40 collet, other times they are in a Grip True adjustable 3 jaw chuck.
These liners that I fit a piston to, are all Aluminum liners hard chrome plated,Except for the F2A speed liners,(they are either bronze or BeCu Beryllium copper)  and have been factory honed and lapped.
Sometimes I do make laps, and re lap the liner a very small amount. But on the most part they are near perfect as they are.
If I am re trimming or reworking an existing piston, then the  mandrel goes into the adjustable 3jaw. If it is a new trim and has like 0.1mm on diameter
or so, then I will often use the ER40 collet to hold the mandrel.
These PCD inserts are the sharpest I have ever come across, and do last quite  along  time so far. I do have a spare insert, but so far have never needed it yet. SO this insert is about 3 to 4 years old now. Only ever gets used for the finish outside passes, and I never use it to trim the end face with it. So I never cut to zero with this insert. For the crown face I use just the regular sharp carbide Al inserts or the Kyocera 06 coated high rake insert. They leave a really good top face finish. Hope t his will help out some people down the track. I have more info in the hints section of the Continuous slide way oiler.
I hand feed the carriage at about 0.01mm per rev or so. so at around 600 rpm, it takes about close to 2.5 mins for a pass down a F2C piston that is about 15mm long. As you feed the tool, you see this very fine sand coming off the workpiece and onto the end of the tool. It can be cut dry, or you can use rice bran oil for a lubricant. Either way, it needs cleaning with break clean to make it very clean to try the piston fit. It also needs to warm back up to room temp as well for the fitting, quite important actually. The chilling of the break clean will result in a smaller piston being fitted, that once warmed up, will be too tight.
Been there and made that mistake.
Neil
« Last Edit: January 11, 2019, 11:06:21 AM by Neil-Lickfold »

Offline Ramon

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Re: Fitting a piston for F2C engine
« Reply #5 on: January 11, 2019, 11:54:13 AM »
Thanks Neil for explaining your processes on this and your other thread   :ThumbsUp:

I don't think I would need to go to this level for the kind of engines I care for but I can fully respect the need to be so accurate for what you do.  Your explanation of 'touch on' is an eye opener - true old saying you can learn something every day if you choose to, as is the sharpness of tooling.

I've been out this morning to give this method a try, albeit on brass and without doing anything to the lathe. I confirm that it does work remarkably well and will shave off micro amounts. I didn't achieve .001 but I did achieve a measurable .002/3 difference on my Mitutoyo mic.

Your comment on hand feeding is noted - I made a larger saddle handwheel some time ago to assist in slow feed like this. Works well but you do have to be careful that your left hand doesn't catch the cross slide handle - yep!

As I was trying that out it occurred that you would be using a high grade of silicon ali for your pistons - the plated liners though would be well beyond my aspirations. That said, like Jim Allen's posts it's really good to hear and see how a professional approach to these matters is carried out.

Measuring kit is the key word too. Save one Geneve clock I don't have the means to measure in microns save that on the Mitutoyo mics - a 'guess' at best, despite how careful the feel. Lapping then provides the means to get accurate fits but not to any defined measurement of course.

You have however been cause for much thought and whilst I think it will still have to be the old lapped cast iron in En1a for me I think I will be approaching matters with your methods firmly in mind

Many thanks indeed

Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline dieselpilot

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Re: Fitting a piston for F2C engine
« Reply #6 on: January 11, 2019, 03:47:09 PM »
Thanks for sharing. Do you also cut a taper at the top of the piston?

I would think a fairly good lathe(Hardinge HLV-H or Schaublin) is needed to make a useful piston like this, especially hand feeding. I have a PCD grooving tool that will take off such thin chips, 1mm wide chips float away. I don't think my old Clausing is in good enough condition to turn the OD of a ringless piston. The highschool students who beat on it previous to my ownership, crashed the chuck into the compound slide so many times it looks like a dog chewed the corner off.

With .01mm/rev and .4mm nose radius theoretical surface roughness well into lapping territory. Real results are completely dependent on the material and cutting edge. The only thing sharper than these sharp edge PCD is monocrystalline diamond. You can cut cast iron with diamond, but CBN is typical. Cast iron is much harder and probably more variable in properties than these aluminum, so the results may not be the same.

Online steamer

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Re: Fitting a piston for F2C engine
« Reply #7 on: January 11, 2019, 04:23:52 PM »
Thanks for sharing. Do you also cut a taper at the top of the piston?

I would think a fairly good lathe(Hardinge HLV-H or Schaublin) is needed to make a useful piston like this, especially hand feeding. I have a PCD grooving tool that will take off such thin chips, 1mm wide chips float away. I don't think my old Clausing is in good enough condition to turn the OD of a ringless piston. The highschool students who beat on it previous to my ownership, crashed the chuck into the compound slide so many times it looks like a dog chewed the corner off.

With .01mm/rev and .4mm nose radius theoretical surface roughness well into lapping territory. Real results are completely dependent on the material and cutting edge. The only thing sharper than these sharp edge PCD is monocrystalline diamond. You can cut cast iron with diamond, but CBN is typical. Cast iron is much harder and probably more variable in properties than these aluminum, so the results may not be the same.

Monocrystalline diamond is usually on Diamond turning lathes, which, although would hold these tolerances at a doddle, aren't really intended for ferrous alloys, but for the optics arena.   0.003" DOC in a diamond turning lathe is considered a very heavy roughing cut!...

PCD, is probably the sharpest tools available for conventional machining, but really require a tight lathe with good geometry.    Sounds like Neil has his tuned well!   A dead sharp tool with have the lowest cutting force. Combine that with a stiff well damped machine structure, and a conventional lathe can work very closely indeed.   I have seen HLV's turn sharpy ink off before....it's always pretty cool to watch that.

Dave
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Damned ijjit!

Offline Ramon

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Re: Fitting a piston for F2C engine
« Reply #8 on: February 01, 2019, 10:30:28 PM »
..................
Actually, The holy grail has been to NEVER EVER lap piston and liner together. They are always lapped separately.


Well Ken - quite a provocative and somewhat surprisingly definitive comment for a first post  :o

All my engines have had piston and liner lapped together but that wasn't my idea - that came from George Aldrich - possibly the most experienced and knowledgeable exponent of piston/liner fit when alive and like yourself, one of the original 'Motor Boys'. For me George was, and still is, very much  a true guru. His treatise on 'Cast in Steel' written in Model Airplane News on making/using cast iron pistons in a leaded steel liner goes into great detail how to carry out this very method and is one carried out on all the engines I've made so far with great success.

I'm aware of your (model engine) background Ken and it may be so in certain situations with other materials but I'm afraid I can't agree with you in making this such a sweepingly positive statement - it's simply not the case.

Regards - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Jo

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Re: Fitting a piston for F2C engine
« Reply #9 on: February 02, 2019, 07:29:33 AM »
Welcome Ken,

Nice to see you join the forum. Would you like to make an introduction post in here: http://www.modelenginemaker.com/index.php/board,3.0.html so other forum members know who you are and your background in making model engines  :)

Jo
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Offline Ramon

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Re: Fitting a piston for F2C engine
« Reply #10 on: February 02, 2019, 08:42:56 AM »
Ken, I should indeed have said welcome to our forum :hi:, Re-reading my post it could be misconstrued as unwelcoming - there was no offence intended I assure you.

Your background in model engine making will readily find a place here  :ThumbsUp:

However, in the past I was asked, and encouraged, by Jo and other members to describe the lapping and honing of small pistons and liners for the benefit of the Forum. As stated at the time it was not the way but my way based on the teachings of George Aldrich. As such it was in direct opposition to your statement - I felt there was no option but rebut your inference that this method was seemingly not acceptable at any cost. Im certain you would agree that there many ways to skin cats - we all have different approaches, this is one of those situations.

Looking forwards to your input on small engines and other matters over coming months  :)

Regards - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Neil-Lickfold

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Re: Fitting a piston for F2C engine
« Reply #11 on: February 02, 2019, 08:53:14 AM »
Model engines are very interesting beasts. In my case if a lapped finish was the ultimate, I would be doing that. Instead I spent considerable time getting my lathe in good enough condition to be able to turn the piston to size. If the engine was a sport engine the effort would be hardly worth it.  Like people have said, many ways to achieve the same end result. Some use sunnen type external hone's.

Offline Ramon

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Re: Fitting a piston for F2C engine
« Reply #12 on: February 02, 2019, 09:13:50 AM »
Sometime ago Neil I bought a Delapena internal honing machine and shortly after, two totally unused  sets of external hones. I have never used the internal - it still sits in a state of re-build, and though I have used the external ones I find a home made brass external lap to be a better and very effective and accurate method of controlling piston size.

The internal laps described elsewhere on here have also provided sterling service over the years giving a high control over the operation but without accurate measuring kit lapping the piston to the bore has been the final operation. The proof is in the pudding so to speak and I can only say that I have had very good success with this method in the engines made so far. The technique used was described sometime ago here http://www.modelenginemaker.com/index.php/topic,1908.0.html. I prefer to lap for all the reasons stated but your method is one I intend to attempt on this next build - begins today BTW ;)

Tug

"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline b.lindsey

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Re: Fitting a piston for F2C engine
« Reply #13 on: February 19, 2019, 05:12:57 PM »
Thanks Ken, and welcome to the forum.

Bill