Suitability of Themac tool Post grinder for cams

[magno_grail]

I built a 90 degree crank for a BSA A65 using XS650 crank parts. I have been waiting over two years for a cam grinder to grind the cam from the blank that I made. I am thinking of making a cam grinder attachment for my lathe. I can rough the lobes with a slab cutter on the CNC mill so it would only be the final finish grind.
Would the Themac tool post grinder be able to handle this, possibly with a diamond wheel?
Thanks.

 

[implmex]

Hi magno_grail:
The likely answer is "sort of"
I say this for a couple of reasons:
First, a lathe, even with a good quality toolpost grinder on it makes a shitty cylindrical grinder in general and an even shittier cam grinder.
This is because the carriage and cross slide are not optimized for grinding..the cross slide pitch is too coarse, they don't weigh enough, you have stiction to overcome, they cannot accommodate multiple steady rests very well, the list goes on and on.
In addition, the grinding wheel on a toolpost grinder is small, so it wears faster, it's harder to optimize coolant flow without trashing the lathe etc etc.

Having said that, it never ceases to amaze me what a determined hobbyist with lots of time, and lots of ingenuity can accomplish, so if you are bloody minded enough to beat your way through this, you may do a usable job, and come out the other side poorer, wiser, and justifiably proud.

But it's never going to be as accurate as a camshaft ground on a proper camshaft grinder, and it'll likely wear the lifters faster too.
There will likely be differences from lobe to lobe, and the question is...does any of that actually matter?
I don't know enough about automotive machining to hazard a guess.

If I really wanted to know, I'd reach out to AlfaGTA who posts on this forum.
He's a vintage car restorer in California whose main thing is automotive machining of all kinds, on the very weird and wonderful world of old classics.
He has a vast knowledge of the details you'd need to know to make a proper judgement.

But my gut tells me a home ground camshaft will be a hacker camshaft...good enough to make it run, but not good enough to make it the best it can be.

With regard to diamond wheels and ferrous metals, the conventional wisdom is that the two are incompatible and you'll trash the diamond wheel very quickly if you try.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

 

[magno_grail]

Since the tool post grinder will only be taking off a few thousanths I would not expect the wheel to wear much. The carriage is only used to locate the grinder over the lobe, not move the grinder back and forth for the lobe shape. That would be done with a rocking mechanism off a master mounted to the collet head.
I will have to put a motor controller on the lathe spindle as the slowest speed is 60 RPM which is far too fast.

 

[CalG]

The spindle on the Themac TP grinder I have is very robust.

IF I cared about the work, I would remove the lathe compound and produce a tool block to more fully support the grinder. I would also carefully analyze the set up for any harmonics or vibrations from both drive belt/pulley, and the wheel it's self. There are several phone applications that make this quite easy . (Not so for the correction however ;-)

A simple water based coolant drip would suffice.

There are many conventional wheels that will do this task. Diamonds are not going to get you anything. Save them for your wife!

 

[implmex]

Hi again magno_grail:
It sounds like you've convinced yourself you want to try to make this work.
If that is true, you will need to adapt the carriage to allow you to mount the toolpost grinder on a linear bearing slide or a swingarm you can tie to a lobe template that rotates with the spindle as you've alluded to.

That part is pretty straightforward.
Be aware though, that on a cam grinder the workhead is the one that swings; not the wheelhead.
That allows a really stiff mounting for the wheelhead, so the wheel can't move even with high wheel forces.
Here's a link to a Youtube video:
CB Performance - Cam Grinder - YouTube

Fortunately though, a BSA motorcycle camshaft is not very long and it is comparatively stout, so you will likely get away nicely with suspending it between a collet and a live center, and won't need steadies.

Developing the proper cam profiles I assume you know how to do, and finding a way to index the cam blank properly so you get the four cam lobes in the proper radial orientation, I assume you also have a plan for.
Do you know how accurate these features need to be?

As I commented before, dedicated cam grinders have big wheelheads, big wheels and what sounds like hard wheels, running in a very rigid setup with a lot of flood coolant to keep the heat down.
The grinding forces are very high compared to normal cylindrical or surface grinding because the entire width of the lobe face is ground at once, and the radial infeed is what controls the force.
Anyone who's ever done plunge grinding on a surface or cylindrical grinder knows that the loads on the wheel go up hugely as the DOC increases or as the WOC increases...with a 1/2" wide wheel in full contact your DOC on a wimpy grinder like a Boyar Schultz or Harig cannot be very deep...of the order of tenths per pass if you want to keep the spindle loads down enough to avoid bogging down the wheel.
The best reasonably sized toolpost grinder is no match for even a Boyar Schultz surface grinder spindle for rigidity, and mounted on a swingarm on a wimpy lathe carriage, I expect it to bounce a bit, just from the slack in the setup.

So you may have to use a very narrow wheel and step it over several times to keep the loads down enough to be successful.
If you don't get the blends perfect from all the stepovers, your lifters will ride on the ridges.

As I said before I don't know automotive machining at all, but I have spent quality time around grinders.
I may be full of shit, and you may be able to ignore all I've said and showcase a brilliant job you can display with pride.

But these are the areas I'd be mentally preparing to overcome if I was contemplating tackling a project like this.
I'd love to hear michiganbuck and eKretz weigh in on this...both have lots of grinder time under their belts too.

Another detail worth considering; from what I've seen of BSA camshafts, the lobes are crowded right together with only a very narrow space between them.
That means your wheel has to run right up to the lobe next to the one you're grinding.
If the setup is even a little bit off, or you get careless, you're going to smack that neighbour lobe into your wheel and the result will be ugly.
Here's a link to a picture:
BSA Replacement Camshafts - SRM / Hepolite - A50 / A65 / A7 / A10

So lots to watch out for and lots to anticipate when you try this.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

 

[michiganbuck]

Here is roughly what it may look like.

BSA Replacement Camshafts - SRM / Hepolite - A50 / A65 / A7 / A10

QT;Suitability of Themac tool Post grinder for cams.

Likely be an ok grinder for a few thousandths.

 

[CalG]

Are BSA cam lobes convex to provide tappet rotation?

 

[Turbowerks]

With the toolpost grinder a 6 inch wheel with a good balance could net you a decent finish. Not sure on that cam but if it uses a tapered lobe for lifter rotation that needs to be plunge ground without traversing but im sure you know that. I grind with a berco cam grinder 54 grit 18 inch wheel. The master cam has to be perfect or you will translate any imperfections onto the cam lobe. Also any runout between the translation wheel, master, master mounting assembly will be multiplied depending on your geometry so take that into account. Sounds like a fun project but going to have a ton of time in the adaptation to get a quality cam imo.


When I find it I don’t need it
When I need it I can’t find it!

 

[magno_grail]

Thanks for the information. BSA followers do not rotate, they are rectangular with a radiused face, side by side, and the block keeps them in line.
For a given duration, lift, follower radius and maximum jerk, the cam profile is quite constrained.
I am not determined to make a cam grinder but I need to move this project along. This first part is to prove the crank will work with a stock cylinder and head, then to cast a new cylinder and head to make it a 750cc.

 

[hanermo]

ANYthing and everything is doable -- even pyramids.

An x axis is quite easily converted to a servo driven screw with 0.5 micron resolution for 1000$ in kit and 200 hours in work.
Later You realise you really need a 2500$ controller to drive it.
I did.
After vast experience -- 2000 production hours, 15 years plus in work, 4 pieces of cheap kit controllers.

A lathe, I believe, can make a great cam grinder.

It´s much more complex than it appears, for endless reasons, and hi-res ac servos and axis ballscrews are the way to go.

There are about 0 public videos and demos of good lathes with high precision x axis, not-cnc, with repeatable results.
Yes, my Very Good old X axis could and did make anything to one-off, but was not good enough for repeat work without probing everything.

You probably need to go full cnc, and should expect to spend 10k++.
? Don´t like it ?
Why does everyone else pay it ?

 

[michiganbuck]

QI: [A lathe, I believe, can make a great cam grinder.]

But a lathe is not designed to shed off grinding grits/abrasive particles and so will allow them more easily to enter critical areas and induce greater wear.

 

[CarbideBob]

Anything can be built.
That in/out rocker is not a easy as it looks.
Pivot distance and wheel size have to be compensated for in the master.

 

[DDoug]

I wonder if this is O.E.M. ?
Or cobbled together ?
Facebook


EDIT:
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So it is OEM.....Who would have thunk it ?

 

[implmex]

Hi digger doug:
Yeah, that Sherline cam grinder is a cute little toy, and for what it is, it does a surprisingly workable job.
Here it is working:
Miniature Sherline CNC Cam Grinder, Part 2 - YouTube

But it sounds like shyte while it's grinding and although the video doesn't show the finish on the cam lobes I'm guessing from the sound it makes when it grinds, that it's pretty bad.
For the hobbyists it's intended for, it's probably more than adequate...that's why I remarked as I did that a cobbled together setup like the OP's considering, can make a "hacker" cam...good enough to make the engine run.

Even so, the wheelhead is stationary on this rig, and as rigid as you can probably get with a Sherline setup.

If the OP wants to start with a lathe and use a toolpost grinder, he's already stacking the deck against himself in my opinion...swinging the mass of the grinder around on a swingarm will only work if he can build it like a brick shithouse and set it up on a reasonably massive lathe.
He doesn't need the swing or the horsepower of a big lathe, but he'd benefit from the mass and rigidity of the carriage and cross slide.

We will see (if the OP follows through with this)...I've been wrong before.
But it's a lot of work to test it out.

BTW, that Sherline setup is about $5000.00

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

 

[greggv]

schnieder cams should be able to help you. They make special one off cams

 

[implmex]

Hi again magno_grail:
Have you considered just mounting the camshaft vertically in a fixture that allows you to support the free end, and using a saw on your CNC mill to just mill the profiles finished?
If you stand up a fourth axis so the platter is horizontal and the axis is vertical, and you put a tailstock on it, you've made something like a camshaft grinder, except you don't need to make a master cam...you can just program it.
If you put a grinding wheel on an arbor in the mill spindle, you could even kiss grind the last couple of thou, and get exactly what you wanted without having to build very much.
You can get the orientation of each cam lobe relative to the others dead nuts correct and get the lobes all as you want them without having to screw around.
Since the BSA camshaft is so short and stout, this would be a viable way forward because your saw (or grinding wheel) arbor doesn't need to be very long to reach all the lobes from the skinny end of the shaft.

If you're willing to start from a big enough piece of stock, you don't even need the fourth axis...you can just stand up the rough bar, mill the lobes one after another, and then pop the blank in the lathe and turn the rest of the features afterward.
The stock has to be stiff enough to get away with that strategy, but steel is pretty cheap...a lot cheaper than buying bits and building a monstrosity for the lathe and fucking around for weeks... all for one camshaft.
If this thing is 6 to 8 inches long and you start with a 3 inch diameter bar you can mill this thing easily right from the solid, and it'll be plenty stiff enough to mill just fine.

So do you have a big enough CNC mill?
Do you have a 4th axis for it?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

 

[eKretz]

I have a buddy who is heavy into custom one-off automotive engine stuff, he's got connections with several big name cam manufacturers. If you just want the cam ground I could probably get you hooked up with someone to do it. Unless you are really out to start making more of your own cams or just want to see if you can do it. (BTDT).

 

[magno_grail]

My plan was to turn the blank with full diameter lobes then hold it upright in the CNC mill and walk around each lobe with a slab cutter. I could leave the long end at the full diameter until the lobes are cut then close finish that end. The base circle is 0.812" and the stock cam lift is 0.385". I want a 0.4" lift. Lift is limited by the block and clearance in the case. With the rocker ratio, having more lift than that results in little increase in flow.
I can get a cam from Megacycle with their grind with 90 degree lobes but when it is non-stock lobe centres their price jumps quite a bit even though the only change is setting the lobe centre.
I may be wrong but when talking to custom shops or big name manufacturers the price is big also.
There is interest in 90 degree cranks in these old engines and most people cut up a crank and bolt it back together but they are still left with a two bearing crank which whips around in the middle although not as bad as a 360 degree crank. My arrangement adds a centre main bearing. So there could be interest in more than a one-off cam.
I have a Haas VF-1 and Slant Jr. CNC machines.

 

[magno_grail]

My plan was to turn the blank with full diameter lobes then hold it upright in the CNC mill and walk around each lobe with a slab cutter. I could leave the long end at the full diameter until the lobes are cut then close finish that end. The base circle is 0.812" and the stock cam lift is 0.385". I want a 0.4" lift. Lift is limited by the block and clearance in the case. With the rocker ratio, having more lift than that results in little increase in flow.
I can get a cam from Megacycle with their grind with 90 degree lobes but when it is non-stock lobe centres their price jumps quite a bit even though the only change is setting the lobe centre.
I may be wrong but when talking to custom shops or big name manufacturers the price is big also.
There is interest in 90 degree cranks in these old engines and most people cut up a crank and bolt it back together but they are still left with a two bearing crank which whips around in the middle although not as bad as a 360 degree crank. My arrangement adds a centre main bearing. So there could be interest in more than a one-off cam.
I have a Haas VF-1 and Slant Jr. CNC machines.

 

[Turbowerks]

Make your cam shaft , shaft then machine your lobes on your cnc out of stock machined the width of your lobes and key them on to the cam (shaft) modular cam so to speak. I have made cam masters this way for my berco. Used a grinding wheel in the mill to kiss the finish after milling as a experiment. It worked ok, good enough to prove a design. Might work for your application.


When I find it I don’t need it
When I need it I can’t find it!