Another Paddleducks build log

[Brass_Machine]

Ya know, for all I do on the lathe... I have NEVER threaded on it. Except using taps and dies anyway. Anyone want to do a thread on it with pictures?? Please?

Eric

[spuddevans]

Tim, I don't know how others get on, but I find single pointing produces far better and squarer threads than dies.

Don't be in too much of a hurry to get those dies in......not for precision work at least....

You're doing a grand job as always...thanks for the write-ups....

Thanks Darren, I believe you are right about single pointing producing far more accurate thread forms. I probably will continue single pointing after I get the tailstock die holder doo-dah made, probably start the thread off single pointing, get it near total depth and then just finish off with a die to get the right form and depth.


By the way, does anyone have a link or know of a publication that has a nice list of thread depth's, I have a couple of charts that give the OD of the different threads along with drill sizes for various %'s of thread depth, but I would really like a chart that tells me what each standard thread depth is, especially for metric threads as that is all I work in at the moment, ie M3 thread depth is ?? M4 is ... and so on and so fifth forth

I keep meaning to pick up a Zeus handbook, maybe it has something like that in it? I'm willing to buy a book that has the relevent details in it, I just dont want to buy a book thinking that it'll have it in it, and then find out it doesnt. So can anyone point me in the right direction please?

Tim


edit,

I just read your message Eric, I'll take even more pics than usual tommorow afternoon when I remake and thread my packing gland nuts screws and try and post up a new thread about it.

[Darren]

Good question Tim....I have no idea, but assumed with metric threads depth was the same as pitch?

I just keep going till the part fits snugly.....but if you have to make both parts I can see that being difficult.
The other way I have done it is by judging with a thread gauge.

[kvom]

A copy of machinery's handbook might be a good investment.  I got a used copy online for about $15.

For the small threads we use in modeling I have been cutting partial threads on the lathe and finishing them with dies.  Even with no undercut at the shoulder, you can use the die to thread almost to the shoulder as Bogs says.  the partial threads cut with the lathe will keep the die straight.

Definitely turn the boss and drill the glands with the same setup on the lathe.  You want the piston rods and valve stems to be dead center going through.

[rleete]

But then again, there is great frustration in single pointing...(multitude of ways to mess it up)

Yeah, we've all had our share of screwing up.  In fact, threading is probably one of the easiest to ruin, as there are so many ways to do it.  You didn't mention the one that's my most common, which is running the tool into the shoulder by not disengaging the leadscrew, and either snapping off the pointing tool, or messing up the shoulder.  Then there's the "forgot at which line to engage the leadscrew", thereby cuttting an entirely new groove right over/through your almost finished threads.

I think that's why I derive so much personal satisfaction in doing it right.


As to the thread depths, someone posted a chart for imperial threads here or over at HMEM.  I printed and laminated it for hanging on the wall, and it's a very handy reference.  Not sure if they did one for metric, but it's worth a look.  If not, you can probably find one on-line with a bit of searching.

[Darren]

Actually for someone who certainly considers themselves to be a complete novice I have found single point threading to be a complete and utter doddle...

Nothing to it....honestly...

Certainly on a 7x12 it is at least.....

[Stilldrillin]

Actually for someone who certainly considers themselves to be a complete novice I have found single point threading to be a complete and utter doddle...

Nothing to it....honestly...

Certainly on a 7x12 it is at least.....

He`s right, you know! 





David D

[spuddevans]

So here's todays update.

I started off by grinding up a new undercutting tool, about 0.8mm wide, here shown with one of the previously made gland adjustment screws for comparison



Then I chucked up the brass hex bar in the 3jaw and turned down a little section for threading using a 6mm round profiling tool.



Then I used the new undercutting tool to, umm, ........ undercut a groove



and then single point threaded a M6 thread ( as promised before, I will post up a new thread with a more detailed explaination of how I single point )



And within a short time I had a little family made up.



After changing over to the ER32 collet chuck that still had the packing gland mounted in it. I centre drilled, drilled and then tapped M6 to 5mm depth as per the plans. ( I had to grind down the tips of the taps as they were quite long and tapered to a point, too long to use in this application)

Then I mounted one of the gland screws and screwed it well in, then tidied up the backside of the screw, and then drilled the two pieces at once to keep concentricity, I drilled them 2.2mm then 2.9mm and finally 3mm.



Then I removed the adjusting screw, then reversed the packing gland and turned down the reverse side to fit the bore. This is the result.



Here is what it looks like in its place.





And that's as far as I got today, next time I will make a 2nd packing gland, and then onwards and upwards umm sideways

I gotta go eat some food, then I'll post up my adventures in threading.


Tim

[bogstandard]

Just one criticism Tim.

If you look at commercially ground threading tools, you will notice that the left hand side is ground away as much as possible. If you did that, you could turn almost to the shoulder without it cutting the chamfer under the screw head.


Bogs

[spuddevans]

Just one criticism Tim.

If you look at commercially ground threading tools, you will notice that the left hand side is ground away as much as possible. If you did that, you could turn almost to the shoulder without it cutting the chamfer under the screw head.


Bogs

That's a good idea, never thought of that, I'll have to grind up a off-centre threading tool. 

On these screws the chamfer was created by the round profiling tool, I thought it looked kinda nice and it had the additional plus of allowing the (oversized) threading tool to get close enough.

But I will definately grind up a better threading tool that'll allow threading closer to a shoulder.


Tim

[Stilldrillin]

Just one criticism Tim.

If you look at commercially ground threading tools, you will notice that the left hand side is ground away as much as possible. If you did that, you could turn almost to the shoulder without it cutting the chamfer under the screw head.


Bogs

That's a good idea, never thought of that, I'll have to grind up a off-centre threading tool. 

On these screws the chamfer was created by the round profiling tool, I thought it looked kinda nice and it had the additional plus of allowing the (oversized) threading tool to get close enough.

But I will definately grind up a better threading tool that'll allow threading closer to a shoulder.


Tim

In my "he`s right" pic, you can see I use a blade type parting tool, ground for small scale screwcutting. 

David D

[spuddevans]

In my "he`s right" pic, you can see I use a blade type parting tool, ground for small scale screwcutting. 

David D

Ahh (goes back and looks at the pic again) I missed that the 1st time I saw your pic. I definitely will grind up something similar the next time I have to single point a thread.

Thanks 

Tim

[Darren]

I missed that too David, thanks for re-pointing it out to us.

I'll be grinding one of those up myself as well.....

[Stilldrillin]

Yer welcome Chaps....... 

Sometimes I`m not sure if, "everyone knows that"...... Or not! 

David D

[spuddevans]

So I got a little more done today. I started by making the 2nd packing gland. I didnt take any pics of this, but here's one of the 2 packing glands in place.



I then made a start on the piston assembly, starting by roughing the pistons to within 1mm of final size, drilled and then tapped M2.5 and then bored 2.5mm 1mm deep to allow the rod to seat properly.



then parted off approx 6mm and repeated to make the other piston.



I then started on the rods, and following on from the single point threading thread I was determined to single point it. However, the chart of gears for my lathe did not list 0.45mm pitch as an option. After some not inconsiderable head scratching and vain calculations I gave up and came indoors to download Mklotz's "Change" program, entered my leadscrew pitch and the change gears that I have and it gave me a solution.

Back out to the workshop and a few mins later I was ready to cut. 1st off I centre drilled the end of the rod and brought up the tailstock with my new ball-raced center. Then it was just a case of making a few passes to get to near depth.



Then I removed the tailstock and finished the thread form off with a Die.

Then did it again for the other piston. Then I assembled the bits with some loctite and set them aside to set.



And that's all I got done today. I'll start on finishing the pistons tomorrow, and then on to the crossheads.


Tim

[kvom]

You will need to thread both ends of the rods, as the other end screws into the crosshead.  I don't know if having the pistons attached will pose a problem with the collet system you're using.

I had real problems getting the pistons to be completely square to the rods.  If your pistons are slightly oversize, then turning them to size with the rods chucked in the collet may be a good solution.

[spuddevans]

You will need to thread both ends of the rods, as the other end screws into the crosshead.  I don't know if having the pistons attached will pose a problem with the collet system you're using.

I had real problems getting the pistons to be completely square to the rods.  If your pistons are slightly oversize, then turning them to size with the rods chucked in the collet may be a good solution.

Thanks Kvom, Fortunately with the ER32 collet system I should be ok with clearance for the piston fitting inside.

I had made a piston and turned it down to exactly the size of the bore before I re-read the instruction book and saw that it was reccomended to leave the pistons about 1mm oversize so that you can attach the rod and then turn the pistons to size and have them perfectly concentric with the rod.

So I remade the pistons oversize.


Tim

[bogstandard]

Looking good Tim, even though it looks like you have masochistic tendencies by single pointing those small threads.


Bogs

[spuddevans]

it looks like you have masochistic tendencies by single pointing those small threads.

You dont know the half of it Bogs 

After threading the 1st rod I really, really, really wished I had a tailstock die-holder.

I think it has moved up the "to-do" list, right the way to the top. 


Tim

[sbwhart]

it looks like you have masochistic tendencies by single pointing those small threads.

wished I had a tailstock die-holder.

I think it has moved up the "to-do" list, right the way to the top. 

Tim

Do I detect another thread on the way 

Real nice bit of work there Tim 

Have fun

Stew

[spuddevans]

Well having the day off today I was able to steal a few hours in the playroom workshop.

I started off with the pistons, I chucked one up in the ER32 collet.



I then turned it to 6mm length, turned the diameter to just be able to fit into the bore, then installed an oil groove. Then I used some 600grit and then 1000grit wet+dry to polish the piston to be a nice snug fit in the bore. ( I also eased the sharp edges off with the same 600grit )


I did the same to the other piston, this one was ever-so-slightly smaller ( to match the ever-so-slightly smaller bore ), and so I marked both the pistons and the bores so that I can match them up again, I used a couple of pop-marks on each part.



I then turned my attention to the crossheads, and after hacksawing some brass to make some smaller brass, I started to clean up and square up the pieces, and then to finally size them.



Here they are marked up and ready for drilling.



I didnt want to just rely on the markings, so I used my edge finder and then used the dials to get to the right position. I then drilled one hole before using the dials to get to the next position. This might seem overkill, but one of the blocks of brass was just slightly smaller than the plans called for, so I marked a datum face on both crossheads and indicated off this datum to get to the hole positions. This would make sure that the holes will be in exactly the right places relative to each other ( if not relative to the sides of the block )



I then drilled the hole in the side of the blocks



Here are the 2 crossheads drilled and ready to mill. Can anyone spot the (almost catastrophic) Boo-Boo?








On the second block ( cunningly labeled "2" in the pic ) I drilled the 2.5mm hole correctly, I then moved over, using the dials, to the correct place on the X-axis, and misread, or miscalculated, my dial position on the Y-axis and drilled the 4mm hole 0.5mm too close to the edge ( the centre was 3.5mm in from the edge instead of the 4mm called for in the plans. )
 

Instantly thoughts of how I was going to rectify this sprang into mind, the 1st one being to silver solder a 4mm brass rod into the hole and then to re-bore in the right place. But after I thought for a while it occurred to me that if I make the other 4mm hole out by the same error I can just position the crosshead rods to match. Hence the numbering of the crossheads.




And that's all I got done today. Stay tuned for more of the same, or rather, different mistakes.


Tim

[kvom]

I can just position the crosshead rods to match.

Before going any further, go and mark the plan for the top plate with the revised dimensions. 

Personally I would just remake that crosshead before doing the milling.   

[spuddevans]

Before going any further, go and mark the plan for the top plate with the revised dimensions. 

Personally I would just remake that crosshead before doing the milling.   

Thanks for that, consider it marked 

I would remake the crosshead but I dont have another lump of brass that is big enough.  But we'll see how it goes, I think the top-plate is one of the next pieces to make so it wont be long til I'm either ecstatic with joy or I'm buying in more brass 


Tim

[bogstandard]

Actually, I think I mentioned that the holes in the top plate should be made slightly larger, purely because this area is the one you are liable to have the most trouble with getting things to run smoothly.

Get the piston rod and crosshead connected, then adjust the rods for a good running position. The main thing that can catch you out, if the threads are not square in the piston rod and crosshead locking nut. They can 'kick' the crosshead out of wack, so only a tweak on them to tighten, rather than a grunt.

Coming along great BTW.

Bogs

[NickG]

Tim, that's coming along great. Nice to see screwcutting as we probably don't see enough of that these days. Something I'm guilty of and I will have to practice to get the most from my lathe.

Also, good commitment as it would have been easy to do the rocking engine first!

Nick