Swifty's build of Nemett Lynx

[Brian Rupnow]

Guys--A word of warning.--I have seen the cam drawing for the Lynx, and unless you have a cad program or are a real geometry maniac, there is very little information on that cam profile. I was able to model it with my 3D software, and can provide any missing dimensions if you want them.---Brian

 

[Jasonb]

There is all the info on the cam needed in the article eg Duration, lift, base radius and flank radius plus the table of offsets if you want to use the same method as you used on the Jaguar. Could also be done with the boring head and rotary table method if Gus does not have Z-axis DRO using the info provided.

J

 

[Brian Rupnow]

Jason--I only looked at the drawing, not any of the specs. I hold by what I say----there is very little info on that drawing to create the cam from.--Brian

 

[Jasonb]

Did you not look at the whole set of drawings? Probably why Malcom included a whole separate drawing page dedicated to just the cam, sheet 14 of 15 which is what all the past builders have used to make the cam from.

 

[Brian Rupnow]

Jason--No, I didn't look at the whole set of drawings. Gus was remarking on how tiny the cams were. I had just made the Jaguar cams, so I looked at the drawing of the Lynx cam to try and get some idea of size comparison. I couldn't tell by looking at the drawing, and as I said, the dimensions that I would use for comparison are not there. There is enough information to generate the dimensions, but you can not tell by just a quick look at the Lynx drawing. I offered to supply any dimensions that Gus might not be able to generate. Gus keeps remarking about his WW2 technology, so I thought I would help him with a couple of dimensions if he needed them.

 

[gus]

Did you not look at the whole set of drawings? Probably why Malcom included a whole separate drawing page dedicated to just the cam, sheet 14 of 15 which is what all the past builders have used to make the cam from.

Hi Jason,

Thanks the reminder. Now looking at Sht 14. Believe my fear of the unknown
is over. Will mill cam using offset and RT. I have a bad habit of misreading and learn by these bad mistakes.


Hi Paul,

Have you got this sheet which comes with instructions. I am not sure it is in the Magazine. Will glad to send over.

 

[Jasonb]

Gus sheet 14 is in the special eddition Vol 3 but it is missing some details, I think the link for the corrected one is at teh beginning of this thread if not let me know and I'll dig it out.

Edit, here it is anyway.

http://www.model-engineer.co.uk/sites/7/documents/NE15iss3.pdf

 

[Swifty]

Hi Gus, yes I have the sheet with the degrees and offsets for the cams, just have to fully understand the steps, I may do a dummy run first with a piece of scrap.

Paul.

 

[Brian Rupnow]

Swifty--Having just traveled this cam road yesterday or the day before I will tell you what worked for me. Center the chuck on the rotary table directly below the center of the quill in the Y axis. With a 3/8" or 10mm endmill in the quill. Set the rotary table to 300 (or whatever Malcolm suggests for the Lynx---it was 300 for the Jaguar). Bring the cutter down and touch off the part to be milled and set the quill vernier to zero. Lock the Y axis--all the milling will be done with the table moving in the X axis. You will have a known dimension from the size of stock you are using to the major diameter of the cam. (I measure that major diameter as 0.472" (12 mm) on the Lynx cam.) Move the table in the X axis until the part is no longer directly below the quill. Advance the quill whatever distance is required to get down to the major diameter and take a cut, then back the part out from under the quill, again moving only in the X axis. This will leave a flat spot on the top of the cam. Then you start with the table, advancing the quill however many mm is called for and turning the rotary table however many degrees are asked for and each time taking a pass under the cutter in the X axis. When you have went completely through the tables, leave the part in the chuck, and don't advance the quill any more. Just rotate the chuck in 1 degree increments and take a cut each time without moving the quill. Eventually you will have worked your way all the way through until your last cut comes tangent with the flank on the other side of the cam. This is majorly tedious business. I never had a true appreciation for how many degrees there were in a circle till I cut a cam using this method.---Brian

 

[gus]

Swifty--Having just traveled this cam road yesterday or the day before I will tell you what worked for me. Center the chuck on the rotary table directly below the center of the quill in the Y axis. With a 3/8" or 10mm endmill in the quill. Set the rotary table to 300 (or whatever Malcolm suggests for the Lynx---it was 300 for the Jaguar). Bring the cutter down and touch off the part to be milled and set the quill vernier to zero. Lock the Y axis--all the milling will be done with the table moving in the X axis. You will have a known dimension from the size of stock you are using to the major diameter of the cam. (I measure that major diameter as 0.472" (12 mm) on the Lynx cam.) Move the table in the X axis until the part is no longer directly below the quill. Advance the quill whatever distance is required to get down to the major diameter and take a cut, then back the part out from under the quill, again moving only in the X axis. This will leave a flat spot on the top of the cam. Then you start with the table, advancing the quill however many mm is called for and turning the rotary table however many degrees are asked for and each time taking a pass under the cutter in the X axis. When you have went completely through the tables, leave the part in the chuck, and don't advance the quill any more. Just rotate the chuck in 1 degree increments and take a cut each time without moving the quill. Eventually you will have worked your way all the way through until your last cut comes tangent with the flank on the other side of the cam. This is majorly tedious business. I never had a true appreciation for how many degrees there were in a circle till I cut a cam using this method.---Brian

Hi Brian,

Sounds humanly possible though a wee bitty tedious but if a best cut cam profile is done to drawing then its like pulling up a 20 kg Grouper with 1 kg sinker from 200 meters sea depth. W/o the fish then pulling up the 1 kg sinker is murder.:rant:
Been studying Malcom's fotos and instructions but got no where than skin depth.
Was good to have a team with members individually working on the Nemett Engines and sharing their experience.th_wavth_wav
I am still stuck with the con-rod but will complete today. Finished con-rod will
look passable.

 

[gus]

Hi Gus, yes I have the sheet with the degrees and offsets for the cams, just have to fully understand the steps, I may do a dummy run first with a piece of scrap.

Paul.

OK.

Will wait for your good news and then proceed. This way the unknowns and fears conquered. Will be next week to work on valves and cams.

 

[Swifty]

The chart shows distances to move the quill up with each increment of rotation. Since I have a knee mill, I will be working by locking the quill and moving the knee, I would rather move the knee up, but if I do it the way stated on the chart I will have to move the knee down. The only trouble with moving the knee down is that I usually overshoot the amount then come back up to the reading required, this prevents any mistake caused by the knee sticking.

Paul.

 

[gus]

The chart shows distances to move the quill up with each increment of rotation. Since I have a knee mill, I will be working by locking the quill and moving the knee, I would rather move the knee up, but if I do it the way stated on the chart I will have to move the knee down. The only trouble with moving the knee down is that I usually overshoot the amount then come back up to the reading required, this prevents any mistake caused by the knee sticking.

Paul.

Hi Paul,

Scratching my head now. All I have is a mini vertical end mill and no DRO.
Looks I may have to cannabalise a cheapy China Digital Caliper to read the quill movment. Will be fun. Failure of which I will fall back on to the
Rupnow H&M Engine cams. The vroom vroom will be no fun.

Also have to rig up the RT get the angle setting for each cut. I have a "Made in Singapore'' Digital Angle Readout. At best will be ''Bush Engineering''.

 

[Swifty]

Gus, can you rig up a dial indicator to set your depths?
Another idea would be to use a digital tire tread depth gauge fron eBay, just like a mini vernier.

Paul.

 

[Brian Rupnow]

Gus--Many years ago I cannibalized a 4" digital caliper and attached it to my quill.This is a good deal, because with the push of a button I can have it read out in millimeters or in inches. It was a very easy change/add on, and you can zero it at any point.---Brian.

 

[AussieJimG]

Gus, can you rig up a dial indicator to set your depths?
Another idea would be to use a digital tire tread depth gauge fron eBay, just like a mini vernier.

Paul.

I have successfully used a dti on its magnetic stand on top of the mill and reading the depth from the top of the drawbar nut (increment by increment while the mill is stationary of coiurse).

Jim

 

[Brian Rupnow]

Gus--Are you really sure you want to shut your mill off and start it again 120 times?

 

[doubletop]

Swifty Tagging along for the ride. It looks like its going well and those rings are easy aren't they? When I refurbished my Simplex loco I purchased 4 rings from the UK at 10 quid each. I was recently given a 1 mtr bar of spun cast iron, allowing for parting off, enough to make 240 Simplex rings. That's nearly NZ$5000 worth! Now I know the score, not a case of making a profit but taking the P155. Back to your build... Pete

 

[gus]

Swifty Tagging along for the ride. It looks like its going well and those rings are easy aren't they? When I refurbished my Simplex loco I purchased 4 rings from the UK at 10 quid each. I was recently given a 1 mtr bar of spun cast iron, allowing for parting off, enough to make 240 Simplex rings. That's nearly NZ$5000 worth! Now I know the score, not a case of making a profit but taking the P155. Back to your build... Pete

Hi Pete,

We can go into mini piston ring mfg biz. Made to order. Minimum 10 pcs at S$3---S$5. Most likely we will do it for an IOU beer for beginners building same size IC Engines.

Bought some 3/4'' rings from USA and they just won't ship to Singapore. Had to have a friend to speed mail out. :wall:

 

[gus]

Gus--Are you really sure you want to shut your mill off and start it again 120 times?

Most likely. Just hope the motor won't pack shop on me.:rant:

Piston just done and cylinder sleeve honed with poor man's equipment.:hDe: