peteh
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Post by peteh on Apr 20, 2012 12:58:57 GMT
Quicky update - 4 out of 6 trailing/tender wheels machined apart from filing. Awaiting 1/4" reamer  |
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peteh
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Post by peteh on Apr 21, 2012 12:21:09 GMT
Another quick update and a question.
All the wheels are cleaned up, filed and just awaiting the arrival of the reamer to finish off.
I then started making the tender axleboxes and dir a major stuff up - drilled a hole on the wrong mark - about 1/2" out of position. I think I just about have enough material left to make the four axleboxes however. However made a good time to stop work today - I find it's never worth continuing after a big error.
Now, as to the question. The cylinder bore is 11/16" and I was wondering if using a reamer would gave as good, if not better, finish than boring. It would seem to be a quicker way of doing the cylinder bores.
Replies on a postcard please ...
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peteh
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Post by peteh on Apr 22, 2012 11:46:48 GMT
Well after yesterdays fiasco on the tender axleboxes I managed to get two good ones made today. Only real hassle was in having to open up the slots I milled where the boxes slide in the frame. The 3mm endmill I have had a noticable chamfer in the last mm so as the grooves are only 1.6mm deep had to be filed to correct profile. I just have enough axlebox material left to make the other two - if I don't make any more mistakes  Attachments:
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peteh
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Post by peteh on Apr 22, 2012 11:47:47 GMT
The two axleboxes sitting on the frame Attachments:
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Smifffy
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Post by Smifffy on Apr 22, 2012 20:42:11 GMT
Bore between centres :-)
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peteh
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Post by peteh on Apr 23, 2012 8:09:26 GMT
Thanks for the feed back smiffy - but why?
We are told to use reamers to produce 'true' circular holes/bores such as for pumps - and yet the cyylinders are just a pump in reverse. Just want to understand the 'why'
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weary
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Post by weary on Apr 23, 2012 8:53:44 GMT
Re: reaming cylinders....
I have reamed cylinders 11/16" diameter with complete success, so it does produce an excellent bore, indeed LBSC often recommended reaming as his standard cylinder finish for small cylinders with boring as the second alternative.
I suspect that boring is preferred by model engineers largely because of the cost and inconvenience of purchasing a 'one-off-use' large reamer.
Regards,
Phil
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Post by Deleted on Apr 23, 2012 8:58:22 GMT
Pete
I've been guilty of slapping a MT2 shank reamer in the tailstock and shoving it down a large drilled hole: this technique is not condusive to round holes in the correct place! Ideally, one should use a 'floating' holder, or at least mount the end of the reamer on a centre in the tailstock, and use a wrench! Another improvement is to 'start' the reamer in a short bored section of the work: but then you might as well machine it properly.....
JB
PS: And Phil is correct: decent reamers cost money...
The following is nicked from the net-
The holder must allow the reamer to “find” the center of the hole or “bell mouthing” of the hole-diameter entrance occurs. Without a radial float, the reamer has to engage a sufficient amount of the hole before it stabilizes in the cut. If the reamer does not stabilize, an oversized or out-of-round hole results
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Post by doubletop on Apr 23, 2012 9:51:29 GMT
.. The following is nicked from the net- The holder must allow the reamer to “find” the center of the hole or “bell mouthing” of the hole-diameter entrance occurs. Without a radial float, the reamer has to engage a sufficient amount of the hole before it stabilizes in the cut. If the reamer does not stabilize, an oversized or out-of-round hole resultsNow you tell me...... Pete |
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peteh
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Post by peteh on Apr 23, 2012 10:51:47 GMT
hanks for those replies guys.
If I am reading it correctly it would seem as though the issue is in keeping the reamer concentric with the drilled hole.
As I can just fit my boring bar in an 11/16" hole I will probably bore it then. However - I will keep my mind open until I get there.
Doubletop - Does this mean you reamed ;D ?
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jma1009
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Post by jma1009 on Apr 23, 2012 18:13:32 GMT
as springbok has so correctly described, reaming big holes isnt easy with our size machines and set ups. in theory a reamed hole should be easy, but in practice it isnt quite that simple. most tail end chucks wont take a 11/16" size reamer, and the force required by using a centre and spanner without a sliding tailstock to avoid slack makes the whole operation rather dicey! my lathe has a sliding tailstock, but big reamers are quite an art to get a concentric finish. if your lathe tailstock chuck will accept 11/16" dia and is truly concentric then give it a go, but very gently and very slow speed and frequent withdrawing to get rid of any swarf. you will need to bore the cylinders in any event within 5 thou of the reamer size (rather than say 1/64"). as springbok says, any inaccuracy requires a degree of float. i'm afraid i do my cylinder bores by boring then make up a wooden rod with wet and dry paper wrapped around of very fine grade (1200) to remove any machine marks and get a good finish. crude but it works!
cheers,
julian
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Post by doubletop on Apr 24, 2012 21:36:18 GMT
Yes I reamed; but this conversation is making me think about what I did and how I did it so I went and checked my 11/16" reamer. It's 2MT so with a 2x3MT adapter it would have gone into my tail-stock. So I must have used the tail-stock feed.
However; I have a slight tight spot at the non piston end of one of the cylinders and you guys have got me thinking that this may be the cause as the reamer would have gone in from the piston rod end.
Pete
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peteh
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Post by peteh on Apr 25, 2012 12:47:45 GMT
That's got me thinking now Pete, I have a 2MT ER32 chuck and a full set of ER32 collets. This means that I could easily hold an 11/16" reamer if required. However, I digress. Managed to get the second pair of tender axle boxes finished today and as a bonus also made the valve spindle guides. These are shown as brass or gunmetal round stock on the plans, with a cross slot cut in the outer face to facilitate tightening with a screwdriver. I made mine from brass hex as I reckon a spanner will be easier to use, especially when the spindle is in place. Attachments:
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Post by doubletop on Apr 26, 2012 9:15:23 GMT
...............as a bonus also made the valve spindle guides. These are shown as brass or gunmetal round stock on the plans, with a cross slot cut in the outer face to facilitate tightening with a screwdriver. I made mine from brass hex as I reckon a spanner will be easier to use, especially when the spindle is in place. The valve gland nut is easy to get to as it sits on top. The piston gland nut less so, as the cross-heads get in the way. You may have trouble getting a spanner in if you made that out of hex. Other than that is a matter of personal preference. Pete |
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peteh
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Post by peteh on Apr 26, 2012 12:45:56 GMT
Thanks for the feedback on my nuts Pete. (could possibly have been phrased better? )
No photo tonight but a little more progress. Cut, filed and drilled the tender horn stays (simple piece of /16x3/16) and also drilled the tender frames ready to tap 8BA.
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Post by doubletop on Apr 27, 2012 5:37:48 GMT
Pete
Keep going, each piece is one step closer to getting it running. Its about the journey and not necessarily the destination.
Pete
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Post by Shawki Shlemon on Apr 27, 2012 9:16:51 GMT
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peteh
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Post by peteh on Apr 27, 2012 12:21:16 GMT
I also agree, for me the pleasure in the creation of a piece of working art. The steaming runs a definate second to that. Fairly disastrous evening today. Snapped my LAST 8BA tap when on the 4th hole of 8. Something else to order Managed to successfully machine the first crosshead blank from some 6mm bar (nearest to 1/4") after that so not a total waste. I am guessing that the tap snapped because I was tapping both frames rivited together but not sure if that would put extra stress on the tap. I was only doing a half turn in followed by a quarter turn out so was not being to rough on the tap as far as I know. |
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Post by Jim on Apr 27, 2012 12:54:59 GMT
Were you using a tapping paste Pete?
I find it makes thread cutting a lot easier as it lubricates the cutting process. Works for me especially with the very fine taps.
Jim
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Post by Shawki Shlemon on Apr 28, 2012 9:31:58 GMT
I don't know about others but I only tap in one direction unless I feel the tap is becoming too tight for its size ( it is a feel thing ) then I remove it clean and contiue , very seldom I do the second step , I do that in all metals including SS , in blind holes I count the turns to avoid bottoming .I of course have snapped a few for all sorts of reasons budt not the method .
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