Epoxy granite metal lathe - videos

[Jon]

Epoxy granite metal lathe. By Robert Steinwandel.

7:57 video:

13:25 video:

18:16 video:

13:38 video:

9:04 video:

8:57 video:

9:08 video:

11:19 video:

14:55 video:

9:44 video:

[Frank S]

A nice job, but he made the same mistake the mini lathe makers do. The spindle is way too short

[tonyfoale]

A nice job, but he made the same mistake the mini lathe makers do. The spindle is way too short

Is your concern the distance between the bearings or is there something else on your mind?

[Frank S]

Is your concern the distance between the bearings or is there something else on your mind?

got it in one. Lathe manufactures of old, used to make the distance between the spindle bearings significantly greater than total swing diameter up to 1 1/2 to 2 times the distance to help control runout and reduce the loading on the rear bearing which could be smaller than the bearing behind the chuck.
Even the manufactures like Southbend, Sheldon and Atlas, who primarily made smaller lathes maintained a slightly longer distance than total swing diameter, but their spindles were slimmer with a smaller overall diameter creating a possibility for flex along its length.
Many of the mini lathes have a spindle length so short the distance between the bearings is only the swing radius, done this way because their thoughts are the lathe since the lathe is small and light weight the cut and feeds will be only a fraction of what a larger lathe is capable of preforming so runout and flex will be negligible or nonexistent in most cases, allowing them to save weight and costs of manufacture.
the Lathe this guy has made out of granite will have great stability for its size due to its mass and the rigidity of the stone the one limiting factor will be the length of the spindle and probably the diameter of the bearing next to the chuck

[tonyfoale]

got it in one. Lathe manufactures of old, used to make the distance between the spindle bearings significantly greater than total swing diameter up to 1 1/2 to 2 times the distance to help control runout and reduce the loading on the rear bearing which could be smaller than the bearing behind the chuck.............

...............the Lathe this guy has made out of granite will have great stability for its size due to its mass and the rigidity of the stone the one limiting factor will be the length of the spindle and probably the diameter of the bearing next to the chuck

One of the reasons that some machines have a large distance between the bearings is to have room for speed change pulleys etc. There is a compromise here behind bearing loading and shaft rigidity. You reduce both bearing loads with greater spacing but you lengthen the spindle which increases its compliance. Bearing loads can be catered for by appropriate bearing selection. In this case the diameter and wall thickness of the spindle would indicate that shaft rigidity should not be an issue. My gut feeling is that this lathe is in a good part of the compromise curve.

This lathe does not have great stability as the video shows. What would concern me about this lathe is its susceptibility to temperature change, stated to be due to the different coefficients of expansion between the bed and steel fittings. Which surprised me because epoxy granite is often stated to have a similar coefficient to steel.

This problem that the builder had with this lathe is of great concern to me because I am currently gathering bits to make a precision surface grinder based on epoxy granite. I just rechecked expansion coefficients and got this based on steel at 100%

Steel 100
Epoxy 425
Granite 60

The epoxy is very high and the granite is low, but what counts is the epoxy granite mix. I did a simple mixture calculation and got proportions for the mix of 89% granite with 11% epoxy which would have the same coefficient as steel. General guidelines for epoxy granite are 90 to 95% granite. I have seen videos of homemade tools which use a much lower percentage, I guess because it needs the right mix of aggregate sizes to fill 90% and also mixing 90% with 10% resin would not be physically easy. I suspect that this lathe has too low a granite percentage, which would explain why the rails bent so much when the temperature changed. This emphasises the importance of getting the correct aggregate sizes ratio and then epoxy ratio. Is pretty easy to test how well you have mixed aggregate sizes to fill 90%. Mix the different aggregate sizes and use water to check the void volume, only then get the appropriate amount of resin mixed.

In the case of the featured lathe the pictures of the bed show that the smaller aggregate, sand, has fallen to the bottom (I guess that was the top when cast) and the larger pieces are at the top, both areas will have too much void space which will need to be filled with excessive resin. The small grains need to be well mixed with the big stuff to fill the voids.

I had been thinking about using solid granite rather than epoxy granite but it needs that ~10% resin to match the coefficient of steel.

[Frank S]

One of the reasons that some machines have a large distance between the bearings is to have room for speed change pulleys etc. There is a compromise here behind bearing loading and shaft rigidity. You reduce both bearing loads with greater spacing but you lengthen the spindle which increases its compliance. Bearing loads can be catered for by appropriate bearing selection. In this case the diameter and wall thickness of the spindle would indicate that shaft rigidity should not be an issue. My gut feeling is that this lathe is in a good part of the compromise curve.

This lathe does not have great stability as the video shows. What would concern me about this lathe is its susceptibility to temperature change, stated to be due to the different coefficients of expansion between the bed and steel fittings. Which surprised me because epoxy granite is often stated to have a similar coefficient to steel.

This problem that the builder had with this lathe is of great concern to me because I am currently gathering bits to make a precision surface grinder based on epoxy granite. I just rechecked expansion coefficients and got this based on steel at 100%

Steel 100
Epoxy 425
Granite 60

The epoxy is very high and the granite is low, but what counts is the epoxy granite mix. I did a simple mixture calculation and got proportions for the mix of 89% granite with 11% epoxy which would have the same coefficient as steel. General guidelines for epoxy granite are 90 to 95% granite. I have seen videos of homemade tools which use a much lower percentage, I guess because it needs the right mix of aggregate sizes to fill 90% and also mixing 90% with 10% resin would not be physically easy. I suspect that this lathe has too low a granite percentage, which would explain why the rails bent so much when the temperature changed. This emphasises the importance of getting the correct aggregate sizes ratio and then epoxy ratio. Is pretty easy to test how well you have mixed aggregate sizes to fill 90%. Mix the different aggregate sizes and use water to check the void volume, only then get the appropriate amount of resin mixed.

In the case of the featured lathe the pictures of the bed show that the smaller aggregate, sand, has fallen to the bottom (I guess that was the top when cast) and the larger pieces are at the top, both areas will have too much void space which will need to be filled with excessive resin. The small grains need to be well mixed with the big stuff to fill the voids.

I had been thinking about using solid granite rather than epoxy granite but it needs that ~10% resin to match the coefficient of steel.

I'll be the first to admit I never watch anyone's videos to their entirety if the video is longer than half a minute. Additionally, I hardly ever put on my head [phones to listen to their dialog, consequentially I did not note anything about expansion issues and wouldn't think there could be much change within the normal range of temperature changes in most shops. where the climate could be controlled within 10 to 20 degrees one way or another, I know where there is a huge lathe made out of concrete with iron rails for the ways that is over 100 years old it is used to make 100 ft long shafts for hydroelectric turbines
I did notice in one of his videos where he used tapered roller bearings for the spindle bearings. A lot of lathes used those but nearly all of them that are of any quality also have an angular contact ball bearing next to the larger roller bearing at the chuck end of the spindle

[tonyfoale]

I'll be the first to admit I never watch anyone's videos to their entirety if the video is longer than half a minute. Additionally, I hardly ever put on my head [phones to listen to their dialog, consequentially I did not note anything about expansion issues and wouldn't think there could be much change within the normal range of temperature changes in most shops. where the climate could be controlled within 10 to 20 degrees one way or another, I know where there is a huge lathe made out of concrete with iron rails for the ways that is over 100 years old it is used to make 100 ft long shafts for hydroelectric turbines
I did notice in one of his videos where he used tapered roller bearings for the spindle bearings. A lot of lathes used those but nearly all of them that are of any quality also have an angular contact ball bearing next to the larger roller bearing at the chuck end of the spindle

I am normally like you regarding watching the videos posted on HMT forum but this one caught my attention because of the apparent similarity to what I plan for my surface grinder, and I watched by jumping along until there was a change in the picture. i did happen upon a section where he remeasured the alignment of the slides and there was a 5 thou vertical bend which he related to a small temperature change between that measurement and the same measurement when he aligned the slides. He then put a sample of epoxy granite in a freezer and measured it cold and room temperature and calculated the coefficient. I forget the value but it was much higher than steel, this can only occur if his resin content was excessive. It is a pity because it is one of the nicest lathe builds that I have seen here in stark contrast to a few of the recent offerings which are just plain crap.

[tonyfoale]

i just noticed that he used 11% epoxy but that was by weight, that is a big difference to 11% by volume and confirms my thoughts about it being resin rich.

[Frank S]

I am normally like you regarding watching the videos posted on HMT forum but this one caught my attention because of the apparent similarity to what I plan for my surface grinder, and I watched by jumping along until there was a change in the picture. i did happen upon a section where he remeasured the alignment of the slides and there was a 5 thou vertical bend which he related to a small temperature change between that measurement and the same measurement when he aligned the slides. He then put a sample of epoxy granite in a freezer and measured it cold and room temperature and calculated the coefficient. I forget the value but it was much higher than steel, this can only occur if his resin content was excessive. It is a pity because it is one of the nicest lathe builds that I have seen here in stark contrast to a few of the recent offerings which are just plain crap.

That makes me wonder if it might not have been fully cured or if it should have been aged for a while even after curing before further processing.
I'm not all that familiar the granite epoxy composite, but I have had fiberglass repairs creep due to shrinkage after they aged a while

[Robert Steinwandel]

Hi Frank and everyone. (Hope this works first post here ever) I may be able to answer some questions about the lathe, although I’d love to hear more as it sounds like you all have quite a bit more experience than I do here.

For the epoxy granite, it’s admittedly been a few months since I’ve thought too much about it but I spent weeks reading the entire cnc zone main epoxy granite thread for the bulk of my research, and based on that I believe 11% by weight is close enough to optimal that chasing lower epoxy percents would have diminishing returns. ckelloug took stiffness measurements on many samples of eg and although around 7-8% by weight was better, 10-11% was very similar stiffness.

The look of the side of my casting looks like a total disaster lol, I absolutely see why you think it had terrible settling problems. I actually switched aggregate sources for one of my sizes of granite, the original source was black the new one white. So it looks like there was bad settling, but that was just me gradually switching to the white aggregate as I ran out of black (graded to the same size range of course).

As for thermal issues, honestly Im very concerned about that as I do not have a conditioned shop to work in, so my temps range from around 10F to 100F through the year. I think I can minimize warp with strips of steel attached to the bottom of the casting so when there’s a temp change it at least has even pressure on the top and bottom and doesn’t tend to “banana” so badly

I’ll stop typing now in case this doesn’t post or something lol, but hopefully that at least clears a few things up I forgot to mention on YouTube!