Hi to you all,l am building a home brew small surface grinder with the grinding head being converted bench grinder with a cup wheel ,mounted on an old lathe bed with a mag chuck mounted on the saddle.My main concern is the grinder will have to go up an down will acme threaded studding an nut be fine enough feed ?,any advice please,would be a great help.
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- Thread starter wesley
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Wesley,
To get any sort of fine feed there are a few ways to do it.
A 40tpi thread will give you the same movement as an imperial mic, but the thread just would not be strong enough to hold the weight of an offhand grinder.
The way to get around it is as they have done on my surface grinder, have a heavier thread, maybe 10TPI, and by using a 4 to 1 reduction gear from the handle to the threaded bar, the handle would be marked up into 100 divisions, so giving you one thou per handle division. If you made a larger handle, say with 200 divisions, then you would be able to work in 0.0005" per division. This is the way they do it on some commercial machines, some of the handles have many hundreds of divisions (1000) and are 12" across and work in tenths (0.0001").
I have seen a few plans for offhand grinders with cupped wheels, but they tend to be of the swing grinder variety, usually made from an old drill press standard.
John
To get any sort of fine feed there are a few ways to do it.
A 40tpi thread will give you the same movement as an imperial mic, but the thread just would not be strong enough to hold the weight of an offhand grinder.
The way to get around it is as they have done on my surface grinder, have a heavier thread, maybe 10TPI, and by using a 4 to 1 reduction gear from the handle to the threaded bar, the handle would be marked up into 100 divisions, so giving you one thou per handle division. If you made a larger handle, say with 200 divisions, then you would be able to work in 0.0005" per division. This is the way they do it on some commercial machines, some of the handles have many hundreds of divisions (1000) and are 12" across and work in tenths (0.0001").
I have seen a few plans for offhand grinders with cupped wheels, but they tend to be of the swing grinder variety, usually made from an old drill press standard.
John
Many thanks for that info,can se a bit of light now on this project,l could l use lathe change wheels to get the gearing right,will look out for some 10 tpi studding,as all l have is 20mm stainless,or 12mm acme,,wheel an handle l can make etc.
BaronJ
Grumpy Old Git.
Hi Wesley,
John is quite right, you would need a fairly substantial thread to support the weight of the grinding head.
just a few off the top of my head thoughts.
You mention that you have some 20 mm stainless, you could use that relatively easily with a bit of thought. You need nut to be able to carry the weight and at the same time have minimal backlash. This could be done in several ways. Make a moulded plastic one pressed into a housing or a nut split down one side and clamp screws or a nut almost cut through and a screw to force the two halves apart slightly. I'm guessing that the acme threaded rod is the leadscrew from the lathe. The half nuts may be able to be modified to do what you want, and would probably be as good if not better than the 20 mm.
As you say you can use gears to get the feed rate, but again there is the introduced backlash to consider. In any case this sounds like an interesting project, I will be interested in how you get on, having given consideration to doing something like this myself, though I don't have an old lathe that I could salvage parts from. I would have to go down the fabrication route.
John is quite right, you would need a fairly substantial thread to support the weight of the grinding head.
just a few off the top of my head thoughts.
You mention that you have some 20 mm stainless, you could use that relatively easily with a bit of thought. You need nut to be able to carry the weight and at the same time have minimal backlash. This could be done in several ways. Make a moulded plastic one pressed into a housing or a nut split down one side and clamp screws or a nut almost cut through and a screw to force the two halves apart slightly. I'm guessing that the acme threaded rod is the leadscrew from the lathe. The half nuts may be able to be modified to do what you want, and would probably be as good if not better than the 20 mm.
As you say you can use gears to get the feed rate, but again there is the introduced backlash to consider. In any case this sounds like an interesting project, I will be interested in how you get on, having given consideration to doing something like this myself, though I don't have an old lathe that I could salvage parts from. I would have to go down the fabrication route.
goldstar31
Well-Known Member
Rack and pinion is my choice! My Stent has what is essentially a Myford lathe one
Norman
Norman
BaronJ
Grumpy Old Git.
Hi Norman,
I would guess that he has already got that in mind for the traverse for the table.
Certainly an interesting project.
goldstar31
Well-Known Member
'Twer not clear, like!'
However if we are onto feed screws, might I suggest 3/8th BSF which is 20 threads per inch-- and t'with them, you can use a 50 tooth gear- said he - laughin' and scratchin'
'Cos that is wot I did.:hDe:
'Yer can use 10TPI studding which old Ned Westbury did on his mill drill but it was left handed and a bit clumsy- like. As I found out!
Many thanks for the help on this project am very grateful ,l do think that l have a bit of 3/8 bsf will have a dig,so if l use a 50t gear what size do l need the other gear to be,you will have to bear with me am new to all this,the grinder unit will be mounted on twin columns with two yokes,and l no its a bit of a pain,but was thinking after each adjustment would have a pinch bolt with thumb screw to help any back lash,hope this makes sense ,but it is the gearing and thread that has me in a spin.
wes
wes
10tpi screw and 100 div handwheel gives you 0.001" per div without the need for a 4:1 reduction.
So may be fine enough or just the larger dia handwheel dial to give 0.0005" divisions
BaronJ
Grumpy Old Git.
Hi Wesley,
I'm curious how did you arrive at the need for twin columns for your grinder ?
If it helps divide 1 inch or 1000 by the number of threads to give you the distance per turn. Gears work the same way, Divide the number of teeth on the big one by the number of teeth on the little one to give you the ratio. Then use that number to determine the gear sizes.
For instance your M20 by 1.5. 25.4 / 1.5 = 16.9 Tpi or 59.17 thou per turn, or 25.4 / 1 = 25.4 Tpi for 1mm pitch, which is 39.37 thou per turn.
HTH.
I'm curious how did you arrive at the need for twin columns for your grinder ?
If it helps divide 1 inch or 1000 by the number of threads to give you the distance per turn. Gears work the same way, Divide the number of teeth on the big one by the number of teeth on the little one to give you the ratio. Then use that number to determine the gear sizes.
For instance your M20 by 1.5. 25.4 / 1.5 = 16.9 Tpi or 59.17 thou per turn, or 25.4 / 1 = 25.4 Tpi for 1mm pitch, which is 39.37 thou per turn.
HTH.
hi baron l came up with the twin columns that way it would be very ridged ,like the yokes on motor cycle forks,plus l have some 40mm fork tubes to use up for the columns,thanks for gear info,but from another posting l dont think l will need gears just the 10tpi thread ,ie 3/4unc, l think the hard bit will be finding an old imperial good sized dial with 100 or better still 200 divisions,but will se what comes up,again thanks
Jason,
You are quite right, sorry about that. I must have got confused while converting from 40 threads to 10 threads.
Thanks for putting us right.
Wesley,
You could make your own scale wheel by going here and print out a scale and stick it around the outside of the handwheel. A bit of maths should get the wheel the exact diameter to stick it to.
http://www.blocklayer.com/Scale-Rule.aspx
John
You are quite right, sorry about that. I must have got confused while converting from 40 threads to 10 threads.
Thanks for putting us right.
Wesley,
You could make your own scale wheel by going here and print out a scale and stick it around the outside of the handwheel. A bit of maths should get the wheel the exact diameter to stick it to.
http://www.blocklayer.com/Scale-Rule.aspx
John
BaronJ
Grumpy Old Git.
Hi Wesley,
Thank you for your notes about the fork tubes. You will have to take some pictures and show how you sre getting on.
The link that John gave is a good one, I've used it several times for various scales. Don't forget to calibrate your printer first, before printing out a scale. I have to use 98% of full size to get a printed inch to measure an inch.
Thank you for your notes about the fork tubes. You will have to take some pictures and show how you sre getting on.
The link that John gave is a good one, I've used it several times for various scales. Don't forget to calibrate your printer first, before printing out a scale. I have to use 98% of full size to get a printed inch to measure an inch.
