Well today I managed to get back out to the workshop for a couple of hours. Since the cylinder liners have now been made it was time to start on the other cylinder fittings, namely the 16 valve liners (yes I am building 2 engines).
Having looked at the plans several times and referred to Edgar T Westbury's article published in Model Engineer (April 1947!) it seemed to me that since the guide must have the valve bore exactly central and to size, it would be better to use the 4 jaw chuck to make them.
I then considered the machining process to make the valve guides and due to their shape the best way forward would be to produce phosphor bronze blanks. These would then be inserted into a special collet (yet to be made) which would allow me to produce all the blanks in one go (see photo of the first trial blank).
The blanks could then be inserted into the collet, which would be set to run true in the 4 jaw chuck. Then the very small 3/32nd" central hole can be drilled and reamed before finally boring the ¼" diameter inset which needs a special HSS tool ground to shape, allowing the bottom radius to be turned.
Whether this is the best way to make the valve guides I am not sure, and if you know a better way then let me know before I start the job in earnest. Edgar's article is very skimpy on making the valve guides and this worries me in case there is an easier way to proceed.......A second question arises in my mind in relation to Edgar's design.
Again I will have to do further research since I cannot see why he would have produced the guide with such a small diameter bottom end. It is only 5/32" in diameter and the valve stem is 3/32" in diameter. Making it larger would have the benefit of allowing a larger diameter valve stem, although that may have an influence on the inlet and exhaust volumes......
I may have missed a very good reason for his design being so, so I decided to put further work to one side on the valve guides until I know more and push ahead instead with the 2 flywheels.
Well this morning I made a start on the valves for the pair of Edgar T Westbury's Seal engines I am building. Its been a while since my last work on this pair for various reasons but at least I managed to make a start on the valves.
I still have to finish the two flywheels but I seem to have had a bit of a block turning these and instead of ruining the good one I am leaving it alone while I start on something else. The valve stems are very small at only 3/32nd " in diameter (about 2.4mm in dia) and with a little apprehension I made a start by first making a pencil drawing from Edgar T's plans. I find this helps as I at least once have had to focus on the dimensions. Also it helps to clarify my approach to machining order.
I decided it would also be useful to refer to the 1947 Article in Model Engineer for guidance as well as several articles published in Model Engine Builder (American Magazine) but in the end I felt more confused with the different approaches and fixtures shown. So a 'trial' valve was the order of the day (my excuse in case it goes wrong.....then it turns into a 'trial' piece!).
I started by chucking some 3/8" diameter free cutting stainless steel before facing it off then centre drilling. Once done I decided to run a couple of light cuts to check the tailstock was in line. After the first cut I found it to be out about 2 thou over the short length so adjusted it until it ran true.
I first brought the length of the valve to the outside diameter of the valve over its length (except for approximately 1/4" at the live centre/tailstock end) to the design size of 9/32nd" (just over 7mm in diameter). Then working back from the chuck, using the digital readouts, I came to the point where further reduction of the stem was required.
Because of the thin stem I made light cuts (many many light cuts) but whilst it was more work at least I hoped to reduce the possibility of the valve stem doing its own thing and perhaps wrapping itself round the cutting tool! When getting close to the finish size I again checked it was parallel and was disappointed to find about a thou and a half of an inch difference! However running the tool along a couple of times brought everything back to where it was.
I decided to change the disposable insert for the final cut and was glad I did since it gave a nice bright surface. I then decided to try some of the micro mesh sanding pads I bought for my pens finishes and was really pleased with the results! Will definitely use these for metal as well now. They did work better with a little lubrication (WD40 sprayed on).
The next task was to cut the 45 degree face and to do this I set my top slide over to 45 deg. I used the DRO again to scribe a finish line on the outside of the untouched bar and when repositioning the cross slide to the face end simply kept cutting until reaching the scribed line. Checking the distance again with the DRO's (and magnifying glasses!).
Because of the small diameter of the stem I used my Proxxon tool with its Dremel quick fit cutting disc to cut the tailstock end but oversized. Once this was done the tool was changed to the parting tool and using the DRO to set the point I parted off the valve with the depth of the head a little oversize.
Next time I am going to make a fixture that will allow me to cut the 8BA thread on the end of the valve and also to face off the valve head to dimension, so not quite there yet but I must admit to being pleased at the first attempt! No doubt there are many failures to come with the next 17 needed (or even this one!) so I must not smile too much yet!
Yesterday was a difficult day. I was really pleased with my first valve and took a lot of time over it! Yesterday I ruined it. Ok, it was always going to be a test piece to sort out the machining stages, but I had hoped it would survive after so many chances to ruin it.
Where did I go wrong? Or, where were the problems discovered if I want to be positive. Well the reduction in length to finished size went well to 1/2 a thou (how accurate can we measure with the tools available to model engineers?) and facing the valve to finished depth also was achieved with the little fixture I made. So the process is now set for the production run. So how did it go wrong?
Looking at the plans I have found yet another error! and one that has **&^^%^&* me off. The write up in Edgar's article brought no comfort on his brief description on making the valves and his plan shows the wrong size BA thread! It reads 8BA and the diameter for cutting 8BA according to British fasteners is 0.086" and the plans shows only one diameter of valve stem, 3/32nd" or 0.09367" a difference of nearly 8 thousandths of an inch!
So when I decided to finish the valve by threading the end it was obviously much too large. With previous experience I know the plans are riddled with errors so I thought it must be perhaps 6BA instead. It was over to the books to find out what BA size came nearest 3/32nd". In the publications there are many data tables and drill sizes for tapping threads but little or no data for threading (well not in my books) however a quick search on the internet found the size of 7 BA nearest but the valve stem was 0.00445" under 7BA. If we go to a thread that is under the stem diameter (and as stated on the plans) then a further 0.00775" need to be removed. This also does not account for a further reduction of between 5 and 10% recommended in some of the literature to stop pushing metal in front of the cut.
Perhaps I should have seen it and checked but I think that the plan should show the reduction in stem diameter, shouldn't it? Another wind up point is the length of the thread is not shown either on the plan or in the article! Measuring against the plan shows it near to 0.250" so that's the plan and I will try the next one with a 1/4" end reduction.
On the positive side I made a suitable collet for holding the valve in the chuck for facing and bring it to finished size. After the messing about with the first valve I decided to make the final collet in brass for durability.
Well today's session I should have made at least 4 valves. In the end silly errors resulted in two being scrapped before finishing. On the plus side the work I did whilst laid down yesterday afternoon, in writing up an aide memoir for machining, worked well.
I decided after completing the first valve proper, that I would treat their manufacture in two phases. The first was to do all the turning on the lathe whilst the second is to thread the end of the valve stems 8BA. The second phase will be to face the valves off to finished size.
Based on today's work rate it will take at least another 4 sessions and some more stainless steel stock! Still more made than I had yesterday.......
Today I managed a session in the workshop and completed (other than cutting a screwdriver slot in the valve faces) the first set of 8 valves. Last night I thought I would change my plan and get something to revolve to spur me on! To that end I ma going to get the valve side completed i.e. the camshaft fitted and working on one engine. To that end I drew up machining methods for the tappets, nuts, valve inserts, and camshaft bearings so that side of the engine works!
So after completing the valves the next items I was going to tackle was the two 1/4" hex nuts per valve. That was until I found I didn't have a suitable drill for the tapping. According to my charts I needed a 1.8mm No. 50 or 0.0709" drill. When going to my numbers drill box the only one missing is ............yep No. 50. So that job was put to one side and instead I decided to make the two camshaft bushes. The first went well enough and was reamed 0.250" and was pleased when it fits the camshaft nicely.
The second bush however produced another problem when checking the main block casting. This one was bought second and had some work done by the previous owner. All the work when checked previously was of a high standard, however the two holes bored previously were not the same. One, the timing end was spot on but the second was slightly oval! So worked stopped on the bush because it will need to be oversized, and the casting set up on my angle plate on the mill and the hole bored circular. When the finished 'round' hole was measured the bush will need to be some 35 thou oversize.
I can't see this will cause any problems yet, but will keep my fingers crossed. I will be using some hardening powder for both the nuts and the tappets, for the first time so that will be interesting. I have had it for a couple of years now and never used it before so if anyone has any tips additional to the 'normal' instructions I have, that would be very helpful.
Yesterday I managed to make the tappets for one engine (8 in all) and they are now awaiting my first attempt at case hardening. To speed up their production I made a tube out of stainless steel to fit over the slot drill I was using. The method worked fine and it didn't take too long to make. However, today I only managed a short time in the workshop and looked at how to cut the chamber in the valve guides with the radius required at there base. I did try and make a special tool out of some drill rod (as the Americans call it) but whilst they worked to a degree I wasn't happy.
That's when my memory kicked in and I remembered the ball nose cutters I have and one was in the correct size of 0.250". A quick check of the radius showed it to be near enough so my previously turned valve guide was mounted in the chuck and when considering how to get to depth the second part of my memory decided to wake up. I have a clamp that I attach to the tailstock and then use a DTI, secured to a small magnetic base, to rest against the clamp so ensuring complete accuracy with depth. Why I didn't use it yesterday for the tappets I do not know!!!
I did not use the ball nose milling cutter directly on the valve guide but drilled it out first just undersized and using the cutter to clean up and cut the bottom radius.
Another plan issue showed itself yesterday when completing the two camshaft bushes. Neither the article or the plans show the angle of the oil holes required in both bushes. Nor does it give the diameter of the hole.
My solution was to use the new digital angle ruler bought from Axminster tools on the plan (see photo). This gave a reading of 33 degrees and measuring the plan showed the hole size o be 1/16". I had a bit of a blonde moment however when working out how best to drill the hole and its chamfered entrance. I thought the best was would be to use my Proxxon drill and stand. So I set the head over to 33 degrees and yes I know you will know but when depressing the stand of course it goes only directly up and down!
Blushing I got out my angle vice and after setting the digital angle meter to zero on the base of the drill stand, I adjusted the vice to the required angle and form then on it was simple.
The next session should see most of the valve guides for this first engine completed. After that as soon as the 1.8mm drills arrive I can complete the two nuts required for each valve before carrying out a new experience for me, case hardening the tappets and nuts. I will cover the experience in a separate section of the website as I have had some advice from a member of the forum I use.
If you don't know it then I can highly recommend the Home Model Engine Machinist forum, especially if you are a novice as they are both approachable and knowledgeable.
As always here are a few photo's that may help explain my ramblings.....
