Help identifying/making gear

[Bpence310]

I could really use some help figuring this out. I have a DSG 4AV lathe that I acquired and I've figured out (partially) why my power feed isn't working. It seems I'm missing a change gear (several actually, but only one that I NEED). In the pictures, I attached the plate that has the setups, and a picture of the gears with them labeled how I believe is correct. It seems I'm missing the gear on "C". I took the gear from "D" and moved it to "C" and now I can get my power feed screw to spin. My problem is that I cannot seem to get the correct information for the gear that I need to either make or buy.

The O.D. of the gear on "D" is approximately 105mm, and the gear on "B" is approximately 112mm. I know a Mod 2 gear is 100mm and a mod 2.25 gear is 115mm. These are 48 tooth gears but I'm unsure if they are 20 deg, 14.5 deg, or some other PA. I have some 14.5 deg gear cutters, but they are the wrong mod, so I don't know any good way to determine which gear cutter to buy.

Right now I'm just trying to get smooth sliding and surfacing cuts, but I would like to be able to make all the threads also, so any insight into what gears I need would be helpful.

If anyone has any insight into what these gears are and how I could make them (which PA/Module cutter to buy) I would greatly appreciate it. I have an arbor and dividing head and milling machine, so I can make them if I just could figure that out.

Thanks for any help!

 

[implmex]

Hi Bpence310:
You can infer some things from the make of the lathe and its vintage:
It's a Dean Smith and Grace lathe (British) and looks pretty old.
Old British machine tools likely were imperial geared and the old PA standard was 14.5 degrees so far as I know.
What I do not know is when they switched to 20 degree PA...sometime in the 1970's or 1980's or thereabouts seems about right to me.

That should give you a starting place to see if you can match what you see with a standard.
The Boston Gear catalogue used to have gear outline templates in it so you could overlay a gear and see if the profile matched a given PA.
There maybe something like that out there you can print off the Internet.
One clue is that low tooth count gears at 14.5 degree PA have skinny tooth roots compared to 20 degree PA gears, so look at gear A and take a guess.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[Bpence310]

Marcus,

Thanks for the reply. I had a feeling it was going to be 14.5 degrees rather than 20, but I wasn't sure. The profile seems to match my mod 1 gear cutters, but they are not the proper size.

Do you have any guess on the "true" module of these? The two gears measure 105mm and 115mm O.D. of which neither match up to a Mod 2 or Mod 2.25 diameter. I think I mistyped those in my original post. Is it that important that the OD is exactly 100mm or 112.5mm, or could I make them slightly bigger or smaller and have them still work the same as intended?

Brian

 

[implmex]

Hi again Bpence310:
Stop thinking "module" and start thinking "diametral pitch"
Stop thinking "100 mm" and start thinking "3.937 inches"

Look here:

Gear Design Equations and Formula | Circular Pitches and Equivalent Diametral Pitches Table

Spur Gear design formula for geometry, pitch, tooth clearance and critical functional data. Circular Pitches and Equivalent Diametral Pitches Table

www.engineersedge.com

You can calculate the DP with the formulas from this page.
Start with what you know:
The gear OD and the number of teeth is a good start.
Pick one of the gears you still have in order to measure, because all of the gears in the train will have the same DP.
Once you know that, you also know what B&S involute form cutter to buy.
The rest you already know how to do.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[jariou]

Here is a way to figure out the pressure angle of a gear.

Lay out an inch long (or more) of a narrow strip of clay. Make it about as thick as the gear tooth depth.

Roll the gear on the clay strip

You should get the impression of a straight teeth rack in the clay. Now, get creative and figure out a way to measure the angle. It should be easier than on the round gear itself because you are now dealing with straight lines.

Jacques

 

[jariou]

Right Marcus, I was doing the same calculation, and it looks like 105mm would be a 12 Dp and the 115mm would be an 11 DP if that exists.

105/25.4/50 = 1/12.0952381..
115/25.4/50 = 1/11.04347826...

Jacques

 

[Bpence310]

Hi again Bpence310:
Stop thinking "module" and start thinking "diametral pitch"
Stop thinking "100 mm" and start thinking "3.937 inches"

Look here:

Gear Design Equations and Formula | Circular Pitches and Equivalent Diametral Pitches Table

Spur Gear design formula for geometry, pitch, tooth clearance and critical functional data. Circular Pitches and Equivalent Diametral Pitches Table

www.engineersedge.com

You can calculate the DP with the formulas from this page.
Start with what you know:
The gear OD and the number of teeth is a good start.
Pick one of the gears you still have in order to measure, because all of the gears in the train will have the same DP.
Once you know that, you also know what B&S involute form cutter to buy.
The rest you already know how to do.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Marcus,

I was only thinking in mm because I made an assumption these would be metric gears coming from GB, but I guess that's not necessarily true.

I'm pretty convinced after looking at the Boston Gears catalog you recommended that these are DP12 PA14.5 gears. The 105mm diameter gear fits nearly perfectly with their DP12 PA14.5 48T gear. The oddball is that 115mm gear (I'm at work, so I can't remember the inch measurements off the top of my head). There's no way the gears have a different DP, so I'm wondering if it wasn't a replacement gear that someone made incorrectly and that could be causing my power feed to knock and bounce. I think I'm just going to make three of the 48T gears so I know they are all the same and be done. Would this "fix" any issues with the gearing? I have several hundred pounds of 6.5in cast iron round cutoffs about 3-4 inches thick. It seems like that's a perfectly acceptable material to make the gears out of since Boston Gears seems to sell them in cast iron, also.

Thanks for all your help, and if you see anything I'm missing, please point it out. I'm just an amateur that is trying to make quality parts, so I have a LOT to learn still.
Brian

 

[implmex]

Hi again Bpence:
British "everything" was Imperial up until the Brits made the switch starting in 1965...likely long after your lathe was built.
That oddball gear is probably a bodged mismatch...as you correctly point out all the gears in the train have to have the same DP to run together.
So your desire to make identical gears of the correct DP is sound, so long as you don't need the odd tooth count for some reduction purpose.
But if it's just an idler gear nobody cares what the tooth count is.

Cast iron makes perfectly acceptable gears for your purpose.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[Bpence310]

Hi again Bpence:
British "everything" was Imperial up until the Brits made the switch starting in 1965...likely long after your lathe was built.
That oddball gear is probably a bodged mismatch...as you correctly point out all the gears in the train have to have the same DP to run together.
So your desire to make identical gears of the correct DP is sound, so long as you don't need the odd tooth count for some reduction purpose.
But if it's just an idler gear nobody cares what the tooth count is.

Cast iron makes perfectly acceptable gears for your purpose.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Marcus,

Good information to have, I really appreciate your time!

On an only slightly related note, do you know if there is a cutter similar to the involute gear cutters that is shaped for 30deg splines? I have a buddy that needs a CV axle remade for a golf cart and the manufacturer pretty much doesn't exist anymore and we can't find the part anywhere. It's a Wonh branded axle, so I'm going to attempt to make him a new one. I drew it out in Solidworks and I'm fairly confident in the drawing I made. You can see in the picture the end that wore off on the right side. I was thinking of just grinding an HSS blank to the profile and using something like a fly cutter to do it, but a cutter like the involute style would be awesome, if they exist. I am working on a way to do hobs, but I'm not quite there yet.

Thanks again!

Brian

 

[Peter.]

I repaired a 90T gear for a DSG about 3 years ago that had one broken tooth. It ws 12DP, 14.5PA.

If you have any of the gears you can easily find the PA. Download a free program called Geardxf. Use it to generate a dxf of the gear you have in both 14.5 and 20 PA. Now open those DXF's ( use eDrawings) and print them in 1:1 scale. Put the gear on the drawing you printed and see which one it matches.

As you can see from the pic below, this DSG gear matched 14.5PA.

 

[Bpence310]

I repaired a 90T gear for a DSG about 3 years ago that had one broken tooth. It ws 12DP, 14.5PA.

If you have any of the gears you can easily find the PA. Download a free program called Geardxf. Use it to generate a dxf of the gear you have in both 14.5 and 20 PA. Now open those DXF's ( use eDrawings) and print them in 1:1 scale. Put the gear on the drawing you printed and see which one it matches.

As you can see from the pic below, this DSG gear matched 14.5PA.

View attachment 380712
View attachment 380713

Peter,

That's an awesome idea! I am absolutely doing that when I get home! Good to know you found them to be 14.5 though. That was my only unknown. Much appreciated!

Brian

 

[johnoder]

Peter,

That's an awesome idea! I am absolutely doing that when I get home! Good to know you found them to be 14.5 though. That was my only unknown. Much appreciated!

Brian

Handy page on the 12DP in the 14 1/2 degree section of change gears

 

[Bpence310]

Handy page on the 12DP in the 14 1/2 degree section of change gears

Yeah that's the same one I found in their current catalog. GD48, it sure isn't $11.25 though. Now, it's $178! Which is why I'll be making three of them instead of buying them.

 

[Halcohead]

You can accurately identify the pressure angle of any involute spur gear by measuring its base pitch, which only requires a pair of calipers and a little math (or a chart). This post here describes it well: https://www.practicalmachinist.com/forum/threads/how-to-determine-a-gears-pa.203860/post-1349610

The short explanation is that different pressure angle gears have dramatically different base pitches, even if they have identical diametral pitches. By measuring base pitch (it's the difference in distance between two neighboring sets of teeth, just make sure your calipers are touching the involute profile of the teeth), you identify the fundamental gear profile, and it's not sensitive to things like modified addendums or backlash.

 

[jpt2go]

It's great to hear there's another person that's acquired a DSG lathe!

Although there's no separate forum on the site for this, there are now over 1200 posts and 61 pages on the Dean Smith Grace Lathe Owners topic in the General forum.
https://www.practicalmachinist.com/forum/threads/dean-smith-grace-lathe-owners.164418/page-61

Cheers,

Jon

 

[wood2steel]

Brian, if end up needing a 14.5 pa gear cutter, let me know. May have a few here that'll cover your needs

 

[Bpence310]

Brian, if end up needing a 14.5 pa gear cutter, let me know. May have a few here that'll cover your needs

Thanks! I'm sending a PM now

 

[Bpence310]

I repaired a 90T gear for a DSG about 3 years ago that had one broken tooth. It ws 12DP, 14.5PA.

If you have any of the gears you can easily find the PA. Download a free program called Geardxf. Use it to generate a dxf of the gear you have in both 14.5 and 20 PA. Now open those DXF's ( use eDrawings) and print them in 1:1 scale. Put the gear on the drawing you printed and see which one it matches.

As you can see from the pic below, this DSG gear matched 14.5PA.

View attachment 380712
View attachment 380713

Just wanted to let you know that I tried your method and it worked perfectly! I had to use Autodesk viewer though. For some reason eDrawings wouldn't scale it properly. To fit on a page it was like 1:30 scale. But I did get it to print righ in Autodesk and it matched up perfectly, so excellent method! Thanks again!

 

[Peter from Holland]

These are change gears
I could imagen PA14.5 dgr gears are more expencive as the 20dgr
And as you seem to be missing several it might be just as easy to change them all for the cheapest gears Eighter DP or Module
Peter

 

[guythatbrews]

Determining PA is easy with the base pitch method Halcohead details.

It's almost always the best way.