Ok it is Dumore tool post grinder
https://www.homemodelenginemachinist.com/attachments/dumore-44-pdf.97647/
https://www.homemodelenginemachinist.com/attachments/dumore-44-pdf.97647/
Tool post grinder
- Thread starter Basil
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Ah! Very good, thank you.
xpylonracer
Well-Known Member
I found it a pain with the compound/topslide angled at a very small number of degrees to reduce travel to get .0001" travel into the work, it is best to calculate the amount to move the saddle to compensate for the towards chuck movement when using the compound or you cut away material at the fwd end of travel but leave some at the start of the cut.
At 45 degrees it's simpler as the fwd travel is the same as in feed, guess that's a good reason to use that angle even though it's not so easy to apply a couple of tenths.
At 45 degrees it's simpler as the fwd travel is the same as in feed, guess that's a good reason to use that angle even though it's not so easy to apply a couple of tenths.
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That's what got me to making an independent dial indicator (post#5). It is direct reading of cross travel DOC increment & eliminates backlash issues & float between dovetail surfaces. Kind of like a fine reading DRO. Even so, a single increment of one tick on a tenths reading indicator = 0.0002" diameter reduction (in an ideal world with no other factors). The downside is the cross slide indicator is relatively coarse, typically 0.001" on most lathes. So each pass I back off the dial a half turn to eliminate backlash, then crept in & then only watch the needle to the dial position & locked the table. If you don't have a table lock I think grinding to any kind a tight tolerance is going to be very difficult. Even engaging the lock can easily displace the table much more than intended DOC, but this may be a function of the lathe locking mechanism. Mine just presses on the gib strip & even so I made mods to minimize unwanted secondary movement.
The angled compound is a good way to make small DOC increments because you are using geometry to your advantage. Its harder to set up an indicator but could be done. I think you would still have to obey backlash & have a predictable lock.
Regular TPGs like Dumore & Themac typically interfere with using tails stock support. Looks like the OPs arrangement works though, which is a big plus.
The angled compound is a good way to make small DOC increments because you are using geometry to your advantage. Its harder to set up an indicator but could be done. I think you would still have to obey backlash & have a predictable lock.
Regular TPGs like Dumore & Themac typically interfere with using tails stock support. Looks like the OPs arrangement works though, which is a big plus.
That's a good solution and I have a similar setup but got a few used Mahr digital electronic indicators off Ebay, about 10 years ago they were around $20 but for some reason they now figure they're worth $100. These indicators measure in 50 millionths and have only +/-0.02 range but I have seen on Aliexpress indicators with 0.00004 resolution(0.001mm)/0.0002(0.005mm) accuracy for the same price but with a 25mm range. Not quite as precise but better range and with a usb port instead of a proprietary port.
With some exceptions the wheel rotates so the nut that fastens the wheel is tightened when grinding, the sparks will go down when grinding externally and up, internally. Here is little more information Tool Post Grinder Resources | Dumore Tool Post Grinders
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Hi Basil,
just for your information, by setting the compund slide angle to 84.25° i.e. an offset of 5.75° from centerline of lathe, the tool feed adjustment using the compund slide is 0.1 of the dial reading, so for a 1 thou' infeed of the cross slide the tool actually feeds in by 0.0001" or 0.0002" on the diameter that is true for all lathes, a simple trig. calculation will confirm. Hope that is a clear explanation.
Stay safe and healthy in difficult times,
TerryD
kop
Well-Known Member
@terryd , Thank You! I had forgotten that one.
I'll just do this without the face-palm gif
...last time on "Dazed and Confused in Front of a Lathe"
The sine of 5.75 degrees is .100(18806161) close enough
The sine of 30 degrees is .5 (exactly)
The sine of 45 degrees is .707(10678118) near enough
The confusion stemmed from that one time when the cross slide dial was marked/calibrated for diameter and the compound for radius. Sorry I don't remember the machine as it was at or near high school years and I'm sure my mind was on something else.
I've been using 5.75/84.25 for decades. It's a great way to divide a bit sharper . Imagine locating coordinates on a Jig Borer in radians....
Then the infamous 30 degree (29.5) compound offset.
Okay , let's just say less than or equal to by a close order.
This is .5 exactly. This turns a compound that indicates diameter to one that indicates radius.
Even on these pages that contain such fine (and appreciated) minds I see this confused and just wrong too many times.
45 degrees is 1/2 90 or ...
Nominally useless for most of what I have or will machine.
Then again I'm an amateur radio enthusiast and .7071 comes up all the time.
@terryd , Thank You again for that synaptic connection
I'll just do this without the face-palm gif
...last time on "Dazed and Confused in Front of a Lathe"
The sine of 5.75 degrees is .100(18806161) close enough
The sine of 30 degrees is .5 (exactly)
The sine of 45 degrees is .707(10678118) near enough
The confusion stemmed from that one time when the cross slide dial was marked/calibrated for diameter and the compound for radius. Sorry I don't remember the machine as it was at or near high school years and I'm sure my mind was on something else.
I've been using 5.75/84.25 for decades. It's a great way to divide a bit sharper . Imagine locating coordinates on a Jig Borer in radians....
Then the infamous 30 degree (29.5) compound offset.
Okay , let's just say less than or equal to by a close order.
This is .5 exactly. This turns a compound that indicates diameter to one that indicates radius.
Even on these pages that contain such fine (and appreciated) minds I see this confused and just wrong too many times.
45 degrees is 1/2 90 or ...
Nominally useless for most of what I have or will machine.
Then again I'm an amateur radio enthusiast and .7071 comes up all the time.
@terryd , Thank You again for that synaptic connection
@terryd , Thank You! I had forgotten that one.
I'll just do this without the face-palm gif
...last time on "Dazed and Confused in Front of a Lathe"
The sine of 5.75 degrees is .100(18806161) close enough
The sine of 30 degrees is .5 (exactly)
The sine of 45 degrees is .707(10678118) near enough
The confusion stemmed from that one time when the cross slide dial was marked/calibrated for diameter and the compound for radius. Sorry I don't remember the machine as it was at or near high school years and I'm sure my mind was on something else.
I've been using 5.75/84.25 for decades. It's a great way to divide a bit sharper . Imagine locating coordinates on a Jig Borer in radians....
Then the infamous 30 degree (29.5) compound offset.
Okay , let's just say less than or equal to by a close order.
This is .5 exactly. This turns a compound that indicates diameter to one that indicates radius.
Even on these pages that contain such fine (and appreciated) minds I see this confused and just wrong too many times.
45 degrees is 1/2 90 or ...
Nominally useless for most of what I have or will machine.
Then again I'm an amateur radio enthusiast and .7071 comes up all the time.
@terryd , Thank You again for that synaptic connection
Hi,
You're more than welcome and thanks for your insight
TerrryD
Back in post #5 Petertha, shows the use of an indicator which looks like tenths reading type.
A low cost digital version of this exists with a 1/2 inch travel, and with the press of a button is inch or millimeter. Resolution to 0.001mm (0.00005").
I searched for "indicator digital electronic". Careful I saw sellers showing 0.001mm indicator photos but were only 0.01mm resolution.
I purchased mine several years ago, the price has gone up. I was using my tool post grinder working on fixing the spindle taper adapter, as it was made wrong as delivered with the lathe.
With the digital indicator, I'm able to control the feed with the cross feed screw to tenths. In my case I'm using the compound slide to machine the taper of this adapter. The last pass I ground was 0.0001, and this was the first time this surface finish appeared. Sorta wood grain in appearance. I've had issues with ripples which are related to wheel balance or spindle vibration. I've increased my lathe's spindle speed to 300RPM and this fixed the ripple pattern I was seeing.
I did a high spot bluing, and I think the spindle headstock taper has some issues as well. It is seating at the top entry, and bottom, but the middle is untouched. Probably good enough. What I fixed was it was bottoming out and it would rock 0.0045 at the top. It was perplexing as it felt like it seated in the hole. But it never kept the 60 degree center that fits in this adapter centered.
https://www.ebay.com/itm/Digital-El...656976?hash=item1a79be3010:g:S5wAAOSw2hhcqsHbThis should be available with UK or Australia eBay sites.
A low cost digital version of this exists with a 1/2 inch travel, and with the press of a button is inch or millimeter. Resolution to 0.001mm (0.00005").
I searched for "indicator digital electronic". Careful I saw sellers showing 0.001mm indicator photos but were only 0.01mm resolution.
I purchased mine several years ago, the price has gone up. I was using my tool post grinder working on fixing the spindle taper adapter, as it was made wrong as delivered with the lathe.
With the digital indicator, I'm able to control the feed with the cross feed screw to tenths. In my case I'm using the compound slide to machine the taper of this adapter. The last pass I ground was 0.0001, and this was the first time this surface finish appeared. Sorta wood grain in appearance. I've had issues with ripples which are related to wheel balance or spindle vibration. I've increased my lathe's spindle speed to 300RPM and this fixed the ripple pattern I was seeing.
I did a high spot bluing, and I think the spindle headstock taper has some issues as well. It is seating at the top entry, and bottom, but the middle is untouched. Probably good enough. What I fixed was it was bottoming out and it would rock 0.0045 at the top. It was perplexing as it felt like it seated in the hole. But it never kept the 60 degree center that fits in this adapter centered.
https://www.ebay.com/itm/Digital-El...656976?hash=item1a79be3010:g:S5wAAOSw2hhcqsHbThis should be available with UK or Australia eBay sites.
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Well, there is another good example of grinding with tail stock support. The motor is elevated up & out of the way & the grinding wheel is of sufficient diameter.
- what is the diameter of that wheel?
- what kind of belt is being used
- what is the power rating & what rpm
I've also wondered about the power feed on a typical import lathe while grinding. When I had a distorted feed bar I was picking up an irregular finish. That all but disappeared when the bar was straightened & other alignment fixes, all factory boo-boos. But grinding probably exaggerates this if the carriage traverse isn't also silky smooth & true. That's encouraging thanks for sharing!
- what is the diameter of that wheel?
- what kind of belt is being used
- what is the power rating & what rpm
I've also wondered about the power feed on a typical import lathe while grinding. When I had a distorted feed bar I was picking up an irregular finish. That all but disappeared when the bar was straightened & other alignment fixes, all factory boo-boos. But grinding probably exaggerates this if the carriage traverse isn't also silky smooth & true. That's encouraging thanks for sharing!
The grinder I purchased new (1991) from Enco, back when they were around. They imported this machine from Czechoslovakia. So everything is metric. It is a Drukov Brno SBMT 2B. The one set of wheels for the main grinder is 150mm OD, with 50mm ID hole. I had made a hub that uses standard 1-1/4" surface grinder wheels, and I got some old used wheels that are 6 inch. I've seen this size on eBay.
There seems to be excess vibration from the motor. And it's probably running 3450 RPM, with the spindle pulley the same as the motor pulley. The belt is a flat belt, about 1-3/4" wide of some sort of nylon material impregnated with something to make is stiffer. It came with a long internal spindle adapter, and 2 smaller ones. I just found a seller in the Ukraine with 3mm and 6mm ID holes for these arbors (wheels need to be 10mm long). I need to make a longer arbor to grind the MT#4 hole true again in this adapter. You know how fun it is to measure and guess at a taper. And there does not seem to be any standards used at least relative to the 3" per foot for many surface grinder hubs. Why would they, everything is metric. I was surprised that I made a hub that fits pretty good. But maybe not, with that wood grain pattern.
The motor I think is around 1/3HP. I did have to balance the wheel. I have one of those disk type balancers. Not sensitive enough. I had gotten that this past summer. I thought of making the leveled knife edge type, but then you need to have a very level surface to set it up. And any nicks or scratches in the arbor or knife edges can give misleading results (and another project that I was not interested in). But I got it balanced enough that the ripples were reduced. The bigger thing was the lathe spindle speed of 300RPM vs the 74RPM of my lowest gear, I started with. I'm thinking the balancer's ball bearings have grease that has dried up, so I'm going to remove the shields from one side, try to degrease with starter fluid spray, and see if that improves its operation.
As for this lathe, it is a 16x40 and weighs 5800lbs. It showed up on Grizzly's web site in 2004, never was in the catalog. I think they imported 6 of them. And from everything I've spent time fixing, it was made with every incorrectly made part that the factory used to make these scrap part machines. It does turn very true. And with good Bison and Pratt Burner chucks, the runout quality is optimum.
Peter, I did make your tool post grinder dresser. With the cantilever height off the lathe bed, I have had gouging problems, as it deflects, then recoils back. My vertical column was made with 1" round bar. The problem may be the clamp on the flat way is not rigid enough. I think with my center height this high I need one that reaches across to the other way. I like that it does not use the tail stock, and as you can see the type that would clamp on the work, would need to be a huge type clamp to fit this spindle adapter.
The number of times I had to crank the compound, which has a 5 inch travel on this lathe, was tiresome to say the least. And I typically would only grind 0.0005" per pass maximum. I learned with the surface grinder, that the expansion would cause an over feed, which after cooling would result in areas of dimples, and blacken burnt steel.
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Interesting stuff ignator thanks for your comments. I've thought about vibration too. When my motor is on I can feel the cross slide becomes 'lively' & the indicator needle does a +/- .001 dance on either side of null position on the tenths indicator. The motor itself feels smooth & balanced but I suspect some micro buzz is flowing through to the spindle because everything is hard mounted. If a motor could be divorced from the spindle, reoriented & mounted with a vibration dampening sheet of neoprene or something so its only connection to the grinding spindle was the belt, maybe that might reduce flow-through vibration & improve finish & control. That's kind of the idea in my head right now. Sourcing a motor isn't too bad, its more about making a making/sourcing a decent spindle. Plagiarized pics show general principle but replace their small grinding wheel with big wheel like yours. I have room for a motor on the far side of cross table & that takes care of TS clearance issues if the spindle is compact.
I assume you mean this wheel dresser? It was mostly orientated around scrap bin stock. The one included in the kit was a clamp on (chuck or part) affair. I don't have a (rotation) spindle lock so wasn't comfortable with any potential movement while dressing. It also never seemed to be in the right position so I came up with this which clamps on the bed. Still on my to-do list is some kind of collar under the dressing tool head so it can swivel around to different positions but still preserve the center height so the diamond remains tangent. I haven't skimmed off more than maybe 5-10 thou but seemed to work ok. Mostly its messy & I'm paranoid about grit so everything is covered. I powerfeed accross it while holding the vacuum nozzle to catch most right at source.
I assume you mean this wheel dresser? It was mostly orientated around scrap bin stock. The one included in the kit was a clamp on (chuck or part) affair. I don't have a (rotation) spindle lock so wasn't comfortable with any potential movement while dressing. It also never seemed to be in the right position so I came up with this which clamps on the bed. Still on my to-do list is some kind of collar under the dressing tool head so it can swivel around to different positions but still preserve the center height so the diamond remains tangent. I haven't skimmed off more than maybe 5-10 thou but seemed to work ok. Mostly its messy & I'm paranoid about grit so everything is covered. I powerfeed accross it while holding the vacuum nozzle to catch most right at source.
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I spent the day grinding the taper of the spindle. It is very hard heat treated steel, and I only have the grinding wheel that came with the machine, some sort of gray coarse vitrified material. I need to research which kind would be good for this sort of hard steel. Then try to find one for the metric arbor.
I think I found the issue with the dressing tool. I have some geometry not quite right with the bottom side "L" clamp. It allows the plate that sits on the top of the way to flex enough.
