Cylinder Bore 7/8" at a depth of 2.5" OR use DOM/CRS ?

[raynerd]

Hello, I was hoping someone could give me some advice. The next project that I am currently planning requires a cylinder bore of 7/8" to a depth of 2.5". I`m really concerned that to that depth I`m going to end up with a taper as I`m going to have to have my boring bar stuck right out! Infact, I`m fairly sure my boring bar won`t stick out that far! I`m also going to have to buy the cast iron material for the cylinder as it is something I don`t have in stock at that length so it is quite expensive if it goes wrong. Do you think this is do`able - should I give it a go.

The reason I ask is becuase on another project log of the same engine build, someone has used DOM steel tubing (drawn over mandrel), I`d never heard of it but I believe in the UK we normally call it CDS seamless or mechanical tubing. So I`ve found it with an ID of 7/8" but sadly at a very larger length which boosts the price up to £30+ which I can`t justify when I only need 2.5". I believe in the USA a few sites offer to sell it by the inch but I just can`t find anyone that will do that over here. I believe this idea of using DOM for cylinder linings has been mentioned over on HMEM.

So I`m a bit puzzled. Do you think I`m being soft shying away from cutting the bore? I just had the worry to start with and then when I saw someone else had thought the same thing and gone a different route to avoid it, it is now concerning me even more.

Any advice apparecited, either where I can get DOM/CRS seamless by the inch from the UK or how to cut such a long bore?!

Cheers
Chris

[sbwhart]

Chris

Is the bore blind or straight through.

The best way to deal with it would be to drill out as much as you can, then bore, but first make ureself a boring bar make it as thick as you can and just long enough to clear the job, at that size you can make the bar from mild steel with a little bit of HSS held in place with a grub screw, a broken centre drill would be ideal, when you come to the finish cut run the same cut through three or four times to get rid of the spring in the bar.

Boring bar second from left is one I made.



Hope this helps

Stew

[raynerd]

Thank you Stew, that was excellent. It is a through bore for a cylinder for a Webster IC engine. I would prefer to try and bore it so I`m glad you recommend that. As you suggested, I have both some broken center drills and also some little bits of HSS that I`ve accumulated in my box so I`ll make my own boring bar as you have shown. Really appreciate the advice.
Chris

[sbwhart]

Chris

I've not made an IC engine but I understand that you need to hone the bore to get a very good finish, but if you're following a set of plans and build log it should tell you this.

Stew

[jim]

i usually get seamless tube off ebay, i've need some odd ball sizes, always managed to find it!

[raynerd]

Hi Jim

Yes, there is some on ebay :
http://shop.ebay.co.uk/i.html?_nkw=seamless+tube+7%2F8&_sacat=0&_odkw=seamless+tube&_osacat=0&_trksid=p3286.c0.m270.l1313
but it is all expensive when I only need a small length. Or at least I consider it expensive, it`ll cost me the same sort of price for enough cast iron bar to make 3 cylinders...i.e get some spare.

Hummm, I just don`t know. I think I`m still going to stick with trying to cut this long bore myself.

Stew -> the fact that it also has to be a good finish is another thing that scares me, I know Brian Rupnow on HMEM said he used a hone on his cylinder. The plans call for a cast iron or leaded steel cylinder with an alloy piston. Brian and others have also used a Viton o-ring so my plan is to do the same!

Chris

[raynerd]

Do you think something like this would be OK for honing the cylinder?

http://cgi.ebay.co.uk/New-Draper-BRAKE-CYLINDER-HONE-25-57mm-HONING-TOOL-/320635354194?pt=UK_Hand_Tools_Equipment&hash=item4aa75b3c52

[sbwhart]

Yes thats the sort of thing, but you can make your own from ally bar, turn the bar just undersize tap the end a sutiable size split it down the middle then put a screw down the end with a tapered head so that it springs it open then use this with fine grinding paste to hone the bore I'm sure you'll find something on this if you do a search.

Stew

[Bogstandard]

You will find that some people over on HMEM know very little, you have already named one, it is more like the blind leading the blind.

If you are going to be using metal piston rings, then you hone the bore. This gives microscopic scratches to the surface of the bore (and also helps to straighten the bore out whilst doing it) which retains oil on the bore surface while the engine is 'bedding' in. After a while, the rings and bore will wear themselves smooth and the scratches will disappear.

For use with o-rings, the bore must be lapped as smooth as possible, because if you hone, the scratches will rip the face of an o-ring to bits, and it will wear away in no time at all.

[Jasonb]

Take a look at my IHC build over on HMEM, I've recently added the cylinder liner. Hope you are not including me there bogs

The liner is 1" bore and 3 1/8" long, you can see that I use a boring bar made from a bit of 3/4" bar, cross drilled for a HSS toolbit and also how I held the bar in my toolpost. I bored it a little under size and then used one of the sprung hones like your link, run it with parafin as this stops the stone clogging, i'm using CI rings.

BTW you will need the two stone hone as the 3 stone is too big for a 7/8 bore if you decide on a honed finish

Jason

[Bogstandard]

Of course not Jason, I know you are OK.

But you must know the sort of people who I am on about. Stealing other peoples plans and ideas, modifying them so that they then won't work, and then calling them their own.

[John Stevenson]

Can't be me, mine don't work before modification.

John S.

[raynerd]

Thanks for replying. I have to admit I do not know the benfits of piston rings in cast or o-rings so I was choosing o-rings as others seem to have used them on the Webster. I wouldn`t know where to start on cast piston rings having never used them (the 10V I have build just runs off a tight fitting piston with some graphited yarn). If my cylinder bore is 7/8", would the piston rings be cut from 7/8" stock as Jason has showed in his pictures and then just split. Likewise, is the groove that they lie in on the piston just a fraction shallower than the depth of the ring so that it pertrudes slightly - otherwise I guess there would be no point in the piston rings)   I have to admit, piston rings are always something that have confused me despite seemingly being fundemental to most engines!!! I can`t quite understand what they offer over a good fitting piston directly in the cylinder!! Clearly I`m missing something.

Thanks for your replies. With regards to cutting the bore in my original question you have convinced me that I can "try" and do this myself! I guess I need to decide what rings I am using so I can lap or hone the bore.   

[Jasonb]

There is quite a bit to making rings but its not too hard.

Basically the ring is turned to an OD that is the same as the bore, split(not cut) you then spring it open, there are formula for the amount and heat the ring up so it takes on teh shape with this opening. You then put it back in teh bore and adjust until you have a small gap between the ends, in the case of my IHC it was 0.003". The base of the groove is a little less than the ID of the ring.

The piston, alloy in my case is 0.005" less than the liner bore which allows for it to expand.

The reason for rings is there is far less contact area than if the piston was a similar fit to teh bore, therefore less friction and you can use alloy pistons so less moving weight and also being sprung the ring will take up any slight wear.

If you can get hold of the early issues of Strictly IC there is a 3 part series on making rings.

Out of interest what type of ring is specified on the original webster design? I wonder weather some people take the O ring option as being a bit squidgy they allow for not being spot on with bore and piston.

Jason

[raynerd]

Jason, the plans just say the following:

PISTON RINGS - 3/32" X .875"
SOURCE: OTTO GAS ENGINE WORKS
(410)-398-7340
2167 Blue Ball Rd
Elkton MD 21921-3330
http://www.dol.net/~dave.reed/otto.html

1/16" wide rings would offer less friction and probably seal just as well -
simply adjust the ring grooves to accomodate

However on his website, under "cons" for the engine, he writes:

"Possibly needs thinner piston rings to reduce drag and friction (1/16" -vs- 3/32")."

Now I know for sure I`ve seen at least 5 or 6 on the web with O-rings and on the Webster website there are a few completed builds mentioned with O-rings.

OK, I better get reading up on making piston rings as this seems the better way to go!

Chris

[Bogstandard]

I think you would be much better off at this time using Viton rubber o-rings. They are a much easier solution for the Webster, rather than trying to learn all the pro's and con's of metal piston rings.

Get yourself a working Webster first, then on say your next build, try for a metal ringed option on another type of engine. Getting it wrong first time around could easily lead to a non runner.

[sbwhart]

Some great information their John when to Hone and when to lap and what rings to use with each method.

Chris I'd go for the the viton ring method for a first build, I looked into cast iron rings I think its one of those things where you have to have the right techniques along with a big helping of nack.

Stew

[raynerd]

OK, thanks a lot, John, Jason, Stew. I`m glad you have suggested that - making CI rings does look a bit tricky for me! 

http://www.btinternet.com/~sylvestris/rings/rings.htm

....and John, thanks for posting your advice -  , I appreciate it.  I`ll let you know how I get on! I hope you think the Webster is a decent choice for my first IC build. It looks simpler than most.

[Bogstandard]

The Webster is a very good first engine, easy to make and not much to go wrong. Plus running engine builds have been well documented.

Another one to consider is Jan Ridders two stroke that uses a vapour carb. A much larger engine altogether.

http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_tweetakt_motor/tweetakt_frameset.htm

John Somers is currently building one, but had trouble getting it started, but when I last talked to him, he said he had mistakenly drilled a transfer hole too small, so he might have got it running by now.

http://start-model-engineering.co.uk/category/jan-ridders-simple-two-stroke/

You start at the bottom of the page and work your way up.

[Dean W]

Hi Chris;
I think you've got good advice here, especially with Bogs' comments, (yes, all of them ; ).
I can offer my two bits, just for something else to think about.  Since the bore for your cylinder goes all the way through, you can
align bore it and have a very good chance of getting a true bore.  The setup looks something like this:



A bar held between centers, which has a cutter held in a small hole somewhere near the middle of the bar.



Your work piece is first drilled undersized through the center, then mounted to the cross slide on the lathe, shimmed up as needed.
Just another way of skinning the cat.

I have to admit, piston rings are always something that have confused me despite seemingly being fundemental to most engines!!! I can`t quite understand what they offer over a good fitting piston directly in the cylinder!!

The piston rings do something the piston cannot do.  They can run against the wall of the cylinder bore with no clearance tolerance.
The piston has to be smaller than the bore, of course, or it simply would not be able to enter it.  Rings, being flexible, can run against
the bore doing the gas sealing chores for good compression in your engine.  
They do other things, but being able to run right against the bore makes them a pretty handy thing.

Good luck with your build!

Dean

[raynerd]

Thank you for the comment Dean. Am I correct in presuming for this method to work, you must ensure that the bar holding the cutter must be dead centre in the hole/bore you have cut ready? And also that this method will just take the final cut to size as there is no adjustment on the cutter? Seems a smart little method - I think I`d be worried about centering the bar in the original bore from the start.

Totally  , I was browsing your site Dean, back in October and saw the Jerry Howell - Propane burner that you have build. I ordered the plans and they arrived yesterday.  another one to go on the growing list, along with the long list of things I`ve build that haven`t run. Sad thing is, I now realise why some aren`t running but I just can`t find time to try and fix them! So anyway, just wanted to say thanks for an excellent writeup and build of the burner!!

Chris

[Jasonb]

You can adjust the cutter length with sone careful use of a micromiter and a bit of calculation. and yes concentricity is important, you could machine something like the pic and use that as a clamp to hold your liner, so long as you don't remove it from teh lathe it will hold the liner spot on.

J

[Rob.Wilson]

Hi Chris

If you decide to go for a boring bar  between centres ,,, it would be well worth making one of these for setting the cutter 



Great little tool ,, only take an hour or so to make , Design came from one of the early MEW mags   ,,, i could look it out if you want 


Rob

[raynerd]

That is bloody genious! I like that a lot. Considering both yourself and Dean have mentioned this method of boring between centres, is this a method I should look into more rather than the standard boring bar that I was intending on using? Would this give me a more accurate bore with a better finish. My concern with this method is still how to ensure that the bar is setup dead centre of the roughed bore/hole in the work piece. Also I would have to think about how I can hold the job on the saddle and adjusting it so that it is centre. I`ll have to try and read into this method a bit more.

I`m collecting my materials (cast iron) tomorrow so I`m eager to cut, but for once I`ll hold back until I`m clear which method to use.

[John Stevenson]

My concern with this method is still how to ensure that the bar is setup dead centre of the roughed bore/hole in the work piece. Also I would have to think about how I can hold the job on the saddle and adjusting it so that it is centre. I`ll have to try and read into this method a bit more.

Turn two tapered bushes that are parallel in the bore and a good fit on the bar. the OD has to be larger than your bore at one end and less than the pilot hole at the other .
Fit these onto the bar, one at one end small diameter facing inwards, then the cylinder / part then the second bush opposite to the first.
push the bushes tight into the cylinder then pack and clamp up in this position.
lastly slide the bushes out the way and either remove the bar and bushes or just tape the bushes to the bar so they can't foul, then fit the boring tool.

Simples.

[Jasonb]

Thats provided your roughed out bore is true to the outside of the liner!! You also need to ensure that your clamping pressure doe snot distort the liner, I assume its about 1/16" wall thickness

I'll mock up the way I did the liner on the engine in my avitar and take a few pics, that wa sdone with a between cts bar


J

[John Stevenson]

Thats provided your roughed out bore is true to the outside of the liner!!

J

Sorry, missed that, I thought it was a cast cylinder, in which case make part of the bore taper out to the OD and register on the OD of the liner, then pack up and clamp.

Using the tapered bushes is standard operation on line boring machines and adjustable reamers with extension pieces on for line reaming.

John S.

[Dean W]

Chris, you got another batch of good ideas for setting up to align bore that cylinder.  I don't have anything
new to add.  I hope you'll show us your progress!

[Jasonb]

Here is the mock up of how I did the liner for the engine in my avitar.

First machine the liner OD and rough out the bore a littel undersize, you can come at it from both ends if your normal bars are not long enough.

Next take a block of wood or laminate up some MDF and bolt this firmly to your cross slide, the top of the wood needs to be on centre height or a fraction below so you may need to pack & shim it up. This block was used on a smaller lathe but I had two bolts in each slot.



Next screw a second block to the first, mark it so it goes back on the same way and put a bit of card between the two blocks.




Now bore a hole through the two blocks of wood, first with progressively larger drill bits in held in the 3 jaw and then switch to your between cts boring bar until you have a snug fit on the OD of the liner.



Its now just a case of loosening the top screws, removing the card and place the liner in the hole, screw back down and the liner will be held concentric to the lathes axis for boring with the between cts bar. DO NOT disturnb the bottom block.

J

[raynerd]

What a fantastic idea - thanks a lot for the suggestion! I`ve no T-slots on my saddle so I`d have to come up with some way of bolting the wooden block down but that really is an excellent idea. So by boring the wooden block you are ensuring your cylinder will be held aligned!

Sorry if this is a stupid question but a few of you have mentioned "liners". As far as I can read into the plans, the cylinder doesn`t have a liner but is just bored straight out of a bar of cast iron. I presume it is exactly the same idea, I just wanted to clarify considering liners have been mentioned a few times.

Chris

[Dean W]

Chris, being your cylinder is made of CI, you don't likely need a liner.  Those are usually used when the outer part of the cylinder
would be made of something like aluminum.  A good material for dispersing heat, but not for a cylinder bore, so a liner would be
pressed in to get the best of both worlds.

Jason, nice demo you put up!

[Jasonb]

Yes, I was forgetting yours is an aircooled engine, just bore the wood to fit the OD of the cylinder.

Liners are often used on water cooled model engines as the cylinder has a hollowed out section for the water to flow through and the liner closes this off, it would likely have been cast in on a full size.

Jason

[raynerd]

Excellent...thanks, I thought it was the case but it was worth checking!

I`m sorry to be a pita, but I do have another questions. I`m just wondering how to ensure that the bore of the cylinder is square to the face so that it aligns properly and the piston does not try and enter at an angle. I presume to ensure that it is square to the bore, facing the cylinder should be ideally be done immediately after or before boring while held in the same position in the wooden block. If this is the case, I can only imagine you can face the front end while held in the wooden block, by flycutting in the lathe?? That would ensure one face (which would be the front) is square to the bore. Am I right with regards to this or is there are better method?

I will have to cut the fins on the cylinder as well, perhaps a good fitting tapered stub or expanding mandrel into the bore and face up both ends from this and also cut the fins at the same time would be another method?

Chris

[Jasonb]

You can machien one end and the OD at the same setting in the lathe chuck. Then bore in your wooden block with teh other untrue end facing teh headstock so you can as you say flycut the end, I would make this end the crank end.

A mandrel would also work, expanding would liekly be best on this size engine and may well hold better against the parting cuts for the fins.

You could always do the fins while the bar is still in the chuck and use a tailstock centre for support, Think I would go this way as you will get the best grip of the work.

Jason

[raynerd]

Jason, sorry, must have missed your reply. Thanks.

When you say, "You could always do the fins while the bar is still in the chuck and use a tailstock centre for support," do you mean when I am taking the cast down to size in the chuck before boring, cut the fins at this stage? I did consider this but was worried that removing material off the outer diameter for the fins would leave less surface area for the wooden block to clamp down on ready for boring.

[Jasonb]

Yes do it before boring so the ctr will go into a ctr drilled hole. Don't think grip will be an issue particularly with hardwood or MDF

J

[NickG]

Chris, have you started your Webster build yet? I missed the fact you were even making one until now. I've often pondered making one. Can't wait to see your build log.

NIck

[raynerd]

Hi Nick, thanks for posting and the interest. Yes, I have started in a way. I`ve got all my materials together including cast iron for the cylinder and also aluminium plate for the base and supports. I`ve got the little spark plug, I just need a M10 x 1 tap! I`ve also got all the details for the gears and spent hours planning and calculating cutting these as I`m making them myself. I`ve roughed out all my materials for the two supports. So I have kind of made a start but nothing to shout home about. When I start boring the cylinder I`ll start a project log. Problem is I opened this thread and got    into boring between centers so I`ve spent the last week making that "Device for setting up for boring" that I posted in Project logs, that is for the cylinder and I`ve also since realised that because my lathe saddle doesn`t have T-slots, I`ve started building like a tool plate that will fasten to the saddle in place of the tool slide so that I can clamp my cylinder down...again for boring between centers. So basically I`ve been making tooling to allow me to start. I`m slow as hell when it comes to machining and I only get a couple of hours every other night if I`m lucky...

You should join me in making one for yourself.... !

[NickG]

I might have a tap you could borrow, not sure if it's 1mm pitch, will check. It's probably better to bore between centres, sure it could be done without though. I get about the same shop time, on a bit of a roll the last few nights but  that's rare!

I am definitely going to do an i.c. soon, I just need to get the 2 poppin's done, the 7 1/4" electric loco and I'd like to re-try the little stirling. So I'm not ready yet, otherwise I'll have loads of started projects and it winds me up a bit thinking about them all!

Things like the gears for instance I wouldn't be able to make so I'd have to find some that were suitable or go for a 2 stroke for my first i.c. maybe.

Nick

[raynerd]

Nick, if my gears work, I`d be sure to save the cutter profiles and it should be easy enough with my cnc rotab to make a few more.... 

[NickG]

Chris,

I remember the Webster being the first i.c. engine I could find plans for on the internet and it had a good build log with it. However, since then I've seen others that I'd like to have a go at. I really set my heart on a hit & miss but some of the linkages appear quite complex / fiddley and difficult to get to work authentically on very small engines so might give that a miss until later in life! I don't know whether you've seen it but I really like Arv's (putputman) Tiny i.c. over on HMEM. A good few people have built it with good results now and it won't cost much material wise.

I think I'll give the Webster another look before I make my decision though as it seems pretty robust and uses stuff like car contact breakers which will help matters. How much was your spark plug if you don't mind me asking? Can you squeeze a normal 14mm car plug in there? I know it wouldn't really look quite right but the webster isn't really designed for aesthetics!

Nick

[raynerd]

Nick, I`ve seen the tiny Ic engine it just looks fiddly but actually my preference is Malcome Stride's - NE15s engine. I want to build that but I just thought it was a bit tricky for a first build. I`ve now got hold of the plans and have read through them and I`m still pleased I`ve gone for the Webster. I`ve only just got my head around how the engine works !! so it`ll be a nice simple first build.

I`m not one for giving advice, I wouldn`t have a clue if you can fit a 14mm car plug - I`m just a lemming, I just follow what others have done! The plans called for a 1/4" x 32tpi plug which are expensive BUT then he changed it later on to a 10mm NGK CM-6 spark plug which most seem to use! It was cheap - £3.50 ish including the postage!
http://cgi.ebay.co.uk/1x-5812-CM-6-CM6-NGK-SPARK-PLUG-/190459015786?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2c583df26a

I don`t see why a 14mm car plug wouldn`t work but for the price, I`d just go with a CM6.

Ignition is the only thing I`ve not got sorted. I`m also going to put some money into a RC carb as they seem to run much better on these.

Webster looks a  nice build but as John mentioned, I also considered and ask Jan Ridders for his plans for the simple IC engine. That looks nice as well but to be honest I have just seen more running Websters and so I presumed I`d get more advice if I got stuck.

Chris
 

[NickG]

The tiny i.c. looks fiddly but I don't think it actually is when you look at the way each component has been designed. I'll probably have to eat my words at some point for that  Is that the nemmet overhead camshaft one from model engineer? I was buying Model Engineer at the time it was serialised and was very interested in it. It looked simple but not sure it was when I started looking at the components and methods involved! I prefer something that'll be a slow runner as well rather than something buzzing away.

Ah right, that's much cheaper than I expected anyway for the 10mm plug! No point bothering with the 14mm one then! I was thinking of making a glow plug for even more simplicity, less stuff required and the plugs look quite realistic. I've seen people make successful spark plugs but I can't see me managing it - buying a proper plug would eliminate the source of another fault for me!!

I also like the Ridders engines - the simple one seems to be the pressure controlled 2 stroke and his vapour carbs seem to work reliably. Hmm, so much to choose from these days!

Nick

[dbvandy]

Chris,

I have just completed my webster build and I used 7/8 id x 1 od DOM for the sleeve and 1 id x 1.5 od 6061 aluminum for the cooling fins.  I also used 6061 t6 for the piston with a 7/8 viton o-ring.  It has about 10 hours on it and is going strong... I have even had it up to 4000 RPM for 10 minutes at a time, but it gets pretty hot.  Here are some pics to help you out...

Doug