Mery 6-stroke kit.

[Jack3M]

Well this information will just have to settle until I am serious about trying to start it. Once further along will get to compression test, at this point would have to make adapter, and the part who's holes I would use to attach this with have not been made yet. Thinking ahead, I like the idea more of dishing out the piston on each end. Someone told me also that the compression should be different for each cylinder and dumb me, I didn't ask how much of a difference. But I bolted up the head with the piston in there for a photo.

 

[Jack3M]

Forgot I had some photos of how I did the packing. I just happen to have an elk hide and use the edges of the hide to get the circles. Used two layers and as can be seen it just 'stuffs' into place.


Got boat issues so didn't fish yesterday. Didn't get much done either as it was back up time. The shaft for the gear got drilled off center, my mill had slipped and had not noticed. The shaft that runs thru there has bushings, so am getting true using them. The distance from the crank to the center is a pretty precise measurement and for gears it is critical to be correct. So made a marking tool.

This goes from center of shaft if you can see the dot to the red dykem down there to mark distance.

 

[larryg]

Someone told me also that the compression should be different for each cylinder and dumb me, I didn't ask how much of a difference.

What you have is two cylinders with different volumes. The cylinder with the rod in it has volumn consumed with the rod so the intake charge is smaller and threrfore will not show the compression pressure as the cylinder without the rod. This is a swag and it may be what "someone" is talking about.

things are looking good

lg
no neat sig line

 

[Jack3M]

Very good, never considered that aspect

 

[Jack3M]

Got in some time. Cleaned up the larger of the two gears and got it ready to cut teeth.
Also got some time to make the gear hob. I get the formulas online on a Utube posting. You need to know DP (Diametric PItch) and PA(Pitch Angle) to make the cutting tool. Then use the formula for the depth of the plunge cut.

First cut the 6 groves to depth with exact distance between each. There is no room for any error doing this or the tool is wasted steel.

Move over to the mill and using a rotory table to make 5 cuts just off center line which gives the proper offset for the teeth.

Lastly come along with a mill bit and cut off the material between the back of the tooth and the next slitting saw cut taking care not to bite the teeth. And then this will need cleaned up on a wire wheel to get rid of the roughs.

This will be heat treated down the raod

 

[Jack3M]

Also am in need of help, described the problem here.
https://www.homemodelenginemachinis...tting-gears-doesnt-go-high-enough-help.31501/
PROBLEM SOLVED.

 

[karlw144]

Jack, enjoying your build as I’m also building a Mery. I had the required cutters to cut my gears so that I didn’t need to make the hob, but I’d like to add that skill. Could you please provide a link to the information you used?

 

[Jack3M]

Part one, with the most important information, the calculations and basic idea


Part two which I didn't need this time


He does make an error later in the FIRST video re: one calculation, ignore that. The stuff he does on the white board is correct. I think was just a slip on his part (the error)

 

[Jack3M]

Edit to above post. I used the machinist manual to get the depth of cut per tooth, I believe that formula is in the second video. I get a different value using the Machinist Handbook formulas.....not a huge difference, the handbook has a range of min and preferred.

 

[Jack3M]

Let me elaborate, to achieve the depth of cut for the tool, I need what the book calls "Whole Depth (Preferred) h1." There is also "Working Depth h2". P is the diametral pitch. Regardless, the value for the depth of cut (h1 or h2)uses a different factor (X). Thus the formula is: h1 (or) h2=X/P. Clear as mud, right?

In my case, I wish to use the h2 factor and thus the formula for a 32 DP gear is as follows: h2=2.250/32 Thus each cut needs to be a total depth of 0.0703125.....Round to your choice, myself I will use 0.073.

The formula in the video (apparently)splits X difference in half for it's value.

I am thinking that the Whole Depth is what I need as the last set of gears I made could have used a little more clearance from greater depth, i.e., Whole Depth and not Working Depth. Thinkin on making an aluminum casting to test for sure that this all is going to work before I cut the cast blanks from the kit.

(This is all based off the 28th edition of Machinerys Handbook) If I misunderstand, please correct me. It helps me to understand to try to explain to others.

Kind of busy next few, so not going to cut anytime soon by the looks of things as I don't want to mess up by stopping part way, any change is total destruction of the blank.

Good nite folks.

 

[Jack3M]

Well between runs of salmon, rainy day, so getting some stuff done. Spent the whole morning tramming the mill, rotory table, and such. Got to starting on the gear today. Immediately had to modify the tool. Should have made it with more cuts. Instead took a grinder to the (shiny) spot to provide relief, else it dug in to the top of the tooth.

Obviously slow going, .01" per pass, with 7 passes to cut a tooth, then release all, do the dividing plate thing, tighten, cut the next. Decided that .07 was good enough as spread was .067-.0703. Small cuts only otherwise blank gets to vibrating if too much of a cut, part just isn't 'solid' and has flex.

 

[PhilL]

More power to you for making the cutter Jack!

 

[Jack3M]

Wellllllll, not sure why, but it didn't come out. You have to do the whole gear to find out on the last tooth if it came out which is an ugly feeling. So ordered another, have a cast wheel that can use for something, just not a gear. Such is life.

 

[PhilL]

Jack, If I may... Order the cutter from Ebay. You should find it for about $20. I'll find the spec when I get home.
I'm affraid there are too many variables involved and there's no adjustment for mesh. You have to be 100% right the first time. The picture I saw above didn't look like the teeth had the right form. They looked very triangle shaped, not gear tooth shaped. Also, they came to a sharp point. Granted, it's a slow speed but these would have been problematic for you I think.

Also, a couple hints on cutting:
1- To prevent getting to the end and realizing you have a choice of one large tooth or 2 small teeth, take the extra time and do a scratch cut on every tooth. A few thousandths is all you need to see what will happen.
2- There is a method of measuring gears called 3 wire measuring. Google will help you here. This takes the guesswork out.

 

[Jack3M]

Phil go ahead and link me to a cutter, I only see full set options for 32dp 14.5 pa, for a 32 and 150 tooth gears. (I do have a suitable 7/8 arbor) I agree the tooth shape is too sharp, which could mean too much depth of cut. The other end of the cut depth spectrum was only .003 less and not sure if that was enough to make the difference. This is not the first time I have made spur gears with similar tool, just not sure what is off here yet.

 

[PhilL]

Well hell... I can't believe my cheap @$$ spent $45 each for those cutters! What was I smoking?
The cutters I have are TTC (Travers) 10-281-320 and 10-283-320. You'll need both the #1 and #3.
I don't have any peperwork for where I got them.

 

[Cogsy]

In the second picture it looks like the top 'tooth' of the cutter is taking almost a full depth cut but the bottom one is barely engaged (if at all). When I've used a similar tool to cut gears the end teeth barely toughed the workpiece. I guess the size of the blank will make a difference but the cutter certainly has to have the center tooth exactly on the centreline of the blank and from the looks your was not. Possibly this is your issue?

 

[Jack3M]

Cogsy, well I thought it was correctly positioned.

 

[Cogsy]

It could just be the angle of the shot. It just appears off to me but it might not be.

 

[karlw144]

When I cut my 150 tooth gear I used packing plates on both sides of the gear blank to reinforce it to reduce vibration and cut full deapth in one pass. I did do a scratch cut first to make sure my indexing was correct. I used the specific cutter, I can’t remember which one (#1 or #3).