Re: [CAD_CAM_EDM_DRO] Re: Cam making....

Hi, i spent 5 years working in an engine shop building motors, i did mostly
rods, this is all spot on info! cul brian f.

----- Original Message -----
From: "Mark Vaughan" <mark@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, March 25, 2007 7:34 AM
Subject: RE: [CAD_CAM_EDM_DRO] Re: Cam making....


> I've plotted many cams, not with a DTI, but from the tappets, lifters, or
> valves themselves. We used to use vernier timing pulleys and spend hours
> getting the cam timed spot on, but most only plotted one lobe, plot all of
> them and you get quite a surprise. I used to build many performance
engines,
> computer model them for the drag strip guys and for the aircraft industry,
> and broke quite a few once believed power limits for a particular engine.
>
> It is not uncommon to find manufacturers cams that are 3 or 4 degrees out
on
> some lobes compared to others, and 20 thou deviation in lift at the valve.
>
> Some of this of course will be engine block machining errors, is the cam
> square to the center line of the block, are all the lifter ports in a
> straight line, and at the same angle etc.
>
> Error on lifter bores isn't too bad, but again a couple of thou error on
the
> cam centre line is not uncommon, and blocks that are several thou taller
at
> one end than the other.
>
> Strangely all the performance blocks I have built have been very square,
but
> my colleagues seem to find plenty that were out of square and quite a few
> heavily warped blocks.
>
> On BL A series blocks it is not uncommon to find a 5 thuo bend being
applied
> to the crank, the crank on these is so weak it seems to survive unless you
> tune the engine. 5 thoughh on a V8 will take the crank out quite quickly,
I
> was brought a 400 Pontiac V8 block that was eating cranks, more than
fuel,
> the journals were over 20 thou out of line, I think it had been cooked at
> some stage.
>
>
>
> So what does all this mean. I suppose in a production block the tolerances
> vary that much, that a little error in the cam is not uncommon. For a race
> engine, it is nice to have everything as accurate as possible, nice square
> block, same height at both end, align bore all the journals etc., but
again
> a little cam error won't make that much difference. Normally the lift is
so
> hi, a few extra or fewer thou won't make much difference, and the angles
are
> normally fiddled with in 10 degree changes, so one degrees which is a
pretty
> big increment to a machinist won't make that much difference. The big
> differences come from bore and deck heights, and matching all the air flow
> paths to get it in and out of the engine as fast as possible whilst
> maintaining even velocity throughout a cross section of the track.
>
> For cams in all if you do the best job you can, it will most likely be OK
>
>
>
> Dr. Mark Vaughan Ph'D. B.Eng. M0VAU
>
> Managing Director
>
> Vaughan Industries Ltd, reg in UK no 2561068
>
> Water Care Technology Ltd, reg in UK no 4129351
>
> Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
> Phone/Fax 44 1872 561288
>
> RSGB DRM111(Cornwall)
>
> _____
>
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Peter Reilley
> Sent: 24 March 2007 23:39
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Cam making....
>
>
>
> I am curious about your method for measuring your existing
> cam. Using a dial indicator to measure the lobe shape will
> not give accurate results unless the radius of the probe
> tip is taken into account. Also, any slop in the indicator's
> stem will contribute to errors.
>
> Are these errors of concern? Perhaps such accuracy in an
> antique engine is not necessary. Is the object just to get the
> engine running and not to get the original horsepower?
>
> Pete.
>
> ----- Original Message -----
> From: "xj5373" <ian.c.haynes@ <mailto:ian.c.haynes%40btinternet.com>
> btinternet.com>
> To: <CAD_CAM_EDM_ <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
> DRO@yahoogroups.com>
> Sent: Saturday, March 24, 2007 6:03 PM
> Subject: [CAD_CAM_EDM_DRO] Re: Cam making....
>
> Well thanks everyone for the excellent advice, what a great group!
> Summarising there is a technique for reverse engineering existing
> cams;
> Rotate in 5 degree intervals, measure with a dti and tabulate then
> input to CAD as a series of lines
> A technique for working from a hand drawn cam;
> Import a scan of the drawing on top of a template made up of radial
> lines at degree intervals using OSNAP intersection to find the points
> To create the cam outline it is recommended to use arcs wherever
> possible then use polylines to fill the gaps.
> To smooth the polylines use the fit command.
> The ideal method though is to draw the cam directly in CAD.
>
> My next step is to get the first sample cam drawing from my colleague
> and see what we are starting with, this is going to take a few days
> though as he is away for a while. I will also investigate CV mode, I
> assume this is CV mode in Mach 3. I have a bit of an issue with my
> DXF conversions of JPEGs coming out as 3D polylines, I need to
> explore converting them to 2D polylines before I can use the fit
> command.
>
> Just out of interest, the plan is to cast the cams in wax then
> assemble them in the wax at the appropriate angles before committing
> to casting. These are for JAP V twins where the inlet and exhaust
> cams share the same shaft.
>
> Dissappointed I didn't see the CNC cam grinder in Ebay, I would have
> put in a bid!
>
> I will give you an update when I get a real drawing to work with.
>
> Thanks again
>
> Ian
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
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