rambo Posted January 12, 2009 Share Posted January 12, 2009 Hi everyone.... i have a Tovaglieri lathe which is a 2nd hand one. been using it for about 3-4 years now and i wanted to know how i could test it to see its precision and accuracy. i wanted to attach a tool post grinder with a DRO for very high precision grinding tolerances.(upto 5 Micron) and was wondering if it was worthy of it or not. any ideas what all i could check and how i could check the same? Quote Link to comment Share on other sites More sharing options...
John B Posted January 12, 2009 Share Posted January 12, 2009 Grinding on a lathe is not advisable, but if you have to do it, protect the slides as best you can. What lengths and diameters will you be undertaking? What metrology tools do you have to inspect / check the machines accuracy? How accurately is the machine set up now? As most lathe beds are worn near to the headstock end, I would suggest putting a long testpiece between chuck and tailstock, possibly using a travelling steady to support it, and take off a series of test finishing cuts, and use a micrometer to assess the accuracy of size along the length of the bar whilst in the machine, this could show up tapering or stepped worn areas, You could then, if you have the facility, using a surface plate and a matched pair of V blocks and a dial test indicator, check for lobing, straightness and ovality. I would also pose the question Why do you need to grind the surface, the size is only going to be as accurate as you can achieve turning, (Unless the grinding attachment has a finer feed thread arrangement than the lathes) and an excellent surface finish can be achieved using the proper tooling, feeds and speeds, along with polishing and burnishing tools. Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted January 12, 2009 Share Posted January 12, 2009 Spindle wear will dictate basic repeatability and deflection that you can achieve then add to that the variation in the carriage and bed. You could turn 10-30 parts and cut them off without making any offsets to the settings then check diameter of the pieces. That will provide a standard deviation, which is a good starting place to determine basic process capability. If the machine runs out .001 or more, you are wasting time installing a TP grinder. Quote Link to comment Share on other sites More sharing options...
trying-it Posted January 12, 2009 Share Posted January 12, 2009 I agree 100% with both previous posts, but want to add a couple additional details. #1) Lathe accuracy can be dramatically influenced by how level and securely a lathe bed is in a shop. My 7' lathe will actually flex with the concrete floor as seasonal temperatures change. This allows the ways to twist slightly and only cure is to re level the lathe again (on all axis) to correct precision cutting accuracy. #2) One of my first factory machining jobs was to precision grind/profile diamond grinding wheels used in the optical lens field. All grinding was performed on a lathe with a tool post grinder and all radii generated through grinding in the freehand mode. Lathe ways were covered with heavy fabric such as shop apron materials and a strong industrial shop vac system was used to collect as much dust as possible. Before covering the ways, all oil was wiped off/dry. After each grinding operation was completed oil was applied in order to float any remaining dust up and all was wiped off again. Ways were re oiled again for regular typical type machining operations, or wiped dry again to begin grinding another piece. Hope this helps! BE safe Quote Link to comment Share on other sites More sharing options...
welder19 Posted January 12, 2009 Share Posted January 12, 2009 5 micron? What are you doing that could require that kind of acuracy? For anyone who doesn't know what a micron is, 1mm is 1000 microns, human hair varies from 60 to 100 micron, on average 40-50 micron is the limit that the human eye can see. welder19 Quote Link to comment Share on other sites More sharing options...
John B Posted January 12, 2009 Share Posted January 12, 2009 Microns are usually surface finish units, 5 micron would be a highly polished surface, and if this was to be a regular item, I would invest in the proper machine for the job. In the past I have produced highly polished bores for hydraulic pistons to be fitted to on lathes, but not by grinding them. External finishes are a different thing altogether. Quote Link to comment Share on other sites More sharing options...
rambo Posted January 14, 2009 Author Share Posted January 14, 2009 Grinding on a lathe is not advisable, but if you have to do it, protect the slides as best you can. What lengths and diameters will you be undertaking? What metrology tools do you have to inspect / check the machines accuracy? How accurately is the machine set up now? As most lathe beds are worn near to the headstock end, I would suggest putting a long testpiece between chuck and tailstock, possibly using a travelling steady to support it, and take off a series of test finishing cuts, and use a micrometer to assess the accuracy of size along the length of the bar whilst in the machine, this could show up tapering or stepped worn areas, You could then, if you have the facility, using a surface plate and a matched pair of V blocks and a dial test indicator, check for lobing, straightness and ovality. I would also pose the question Why do you need to grind the surface, the size is only going to be as accurate as you can achieve turning, (Unless the grinding attachment has a finer feed thread arrangement than the lathes) and an excellent surface finish can be achieved using the proper tooling, feeds and speeds, along with polishing and burnishing tools. well, i need to grind the surface for shafts with dimensions of 150mmX1500mm and upwards. that is the requirement of my client. moreover, the other lathes i have aren't good enough to handle such a delicate task. or i should say they are worse for the wear than this one. Spindle wear will dictate basic repeatability and deflection that you can achieve then add to that the variation in the carriage and bed. You could turn 10-30 parts and cut them off without making any offsets to the settings then check diameter of the pieces. That will provide a standard deviation, which is a good starting place to determine basic process capability. If the machine runs out .001 or more, you are wasting time installing a TP grinder. sure. i will try this method out. actually, it had struck me to do this before but i wasnt sure if it would give me anything firm as a result. now that i have recommendation from u i will go ahead. I agree 100% with both previous posts, but want to add a couple additional details. #1) Lathe accuracy can be dramatically influenced by how level and securely a lathe bed is in a shop. My 7' lathe will actually flex with the concrete floor as seasonal temperatures change. This allows the ways to twist slightly and only cure is to re level the lathe again (on all axis) to correct precision cutting accuracy. #2) One of my first factory machining jobs was to precision grind/profile diamond grinding wheels used in the optical lens field. All grinding was performed on a lathe with a tool post grinder and all radii generated through grinding in the freehand mode. Lathe ways were covered with heavy fabric such as shop apron materials and a strong industrial shop vac system was used to collect as much dust as possible. Before covering the ways, all oil was wiped off/dry. After each grinding operation was completed oil was applied in order to float any remaining dust up and all was wiped off again. Ways were re oiled again for regular typical type machining operations, or wiped dry again to begin grinding another piece. Hope this helps! BE safe yep. it helps. the only trouble is, in india there is a lot of dust in the air so keeping the bed clean is only a dream. which is y there are some fine lines on the slides. still, im going to try the suggestions above to check how accurate the lathe is for a simple job and then decide on the option of going for a grinder tool post.5 micron? What are you doing that could require that kind of acuracy? For anyone who doesn't know what a micron is, 1mm is 1000 microns, human hair varies from 60 to 100 micron, on average 40-50 micron is the limit that the human eye can see. welder19 well, mostly for grind finishing for a large shaft. Microns are usually surface finish units, 5 micron would be a highly polished surface, and if this was to be a regular item, I would invest in the proper machine for the job. In the past I have produced highly polished bores for hydraulic pistons to be fitted to on lathes, but not by grinding them. External finishes are a different thing altogether. yep. it is external finishing for the job which has to be a grind finish to a tolerance of 5 microns and maybe lesser in some cases. Quote Link to comment Share on other sites More sharing options...
John B Posted January 14, 2009 Share Posted January 14, 2009 What dimensional accuracy and tolerances are required on these shafts? What raw material in which particular condition are they made from? 150mm (diameter?) x 1500mm is quite a chunky piece for that kind of surface finish, and particularly being produced on a machine not really designed to produce this quality of finish, There may be a possibility of achieving that kind of finish using a roller burnishing tool, but this could involve some experimentation on your part. Quote Link to comment Share on other sites More sharing options...
rambo Posted January 19, 2009 Author Share Posted January 19, 2009 hmmm well we are always up for experimentation... the hammer we put up kinda proves it. hehe. i know the dimensions are big, but its a standard sized shaft for heavy machinery. the raw material is carbon steel. they are machined after being forged to margins for machining. Quote Link to comment Share on other sites More sharing options...
John B Posted January 19, 2009 Share Posted January 19, 2009 If I understand the "machined after being forged to margins for machining" means you are premachining the forging prior to finish machining? In which case you should be heat treating the forging first to stress relieve, then 'roughing down' making them then ready for finishing. By yourself, or your client You should be able to achieve a satisfactory finish to close tolerances with the correct feeds and speeds for the type of cutting tools you are using. Subject to lathe condition, Use of steadies may be helpful. Quote Link to comment Share on other sites More sharing options...
rambo Posted January 20, 2009 Author Share Posted January 20, 2009 ya, i guess i omitted to say that we do heat-treat the material after rough machining the forged pieces. since till now our clients have been doing the finishing, we didnt have to bother any further, but now that we want to do the finishing, i asked the question. But thanks for all the info. i am yet to carry out the tests for the lathe to see its current accuracy before i can take a decision on whether i can even do the finish machining on the current lathes or not. :) Quote Link to comment Share on other sites More sharing options...
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